Here is the official support document released by Apple. I found it immensely helpful, may others will too. Maybe sticky it?
http://support.apple.com/kb/HT4895
Summary
An Apple ID is the email address you use as a login for just about everything you do with Apple, including using iCloud to store your content, buying songs from the iTunes Store, and downloading apps from the App Store.
When you set up your iPhone, iPad, or iPod touch, you use the same Apple ID for iCloud services and purchases on the iTunes Store, App Store, and iBookstore. You can, however, use one Apple ID for iCloud services and another Apple ID for store purchases (including iTunes in the Cloud and iTunes Match). You will get all the benefits of iCloud whether you use the same Apple ID for iCloud and store purchases, or different IDs for each.
Products Affected
iCloud
For guidance on which AppleID you should use when setting up iCloud, please see the sections below that apply to you:
Using the same Apple ID for Store purchases and iCloud (recommended)
Using the same Apple ID for store purchases and iCloud is recommended for most users. To use the same ID, follow these steps:
iPhone, iPad, or iPod touch:
When you first set up your iOS 5 device, enter the Apple ID you use for iTunes in the setup screens. It will be used for store purchases and iCloud.
If you skipped the setup process, enter your Apple ID in Settings > iCloud and Settings > Store.
Mac: Enter the same Apple ID in Apple () menu > System Preferences > iCloud and in iTunes > iTunes Store.
PC: Enter the same Apple ID in Control Panel > Network and Internet > iCloud and in iTunes > iTunes Store.
Using one Apple ID for iCloud and a different Apple ID for Store Purchases
You can use different Apple IDs for iCloud and store purchases and still get all of the benefits of iCloud. Just follow these steps:
iPhone, iPad, or iPod touch:
When you first set up your iOS 5 device, enter the Apple ID you want to use with iCloud. If you skipped the setup assistant, sign in to Settings > iCloud and enter the Apple ID youd like to use with iCloud.
In Settings > Store, sign in with the Apple ID you want to use for store purchases (including iTunes in the Cloud and iTunes Match). You may need to sign out first to change the Apple ID.
Mac:
Enter the Apple ID you want to use for iCloud in Apple () menu > System Preferences > iCloud.
Enter the Apple ID you want to use for store purchases (including iTunes in the Cloud and iTunes Match) in iTunes > iTunes Store
PC:
Enter the Apple ID you want to use for iCloud in Control Panel > Network > Internet > iCloud.
Enter the Apple ID you want to use for store purchases (including iTunes in the Cloud and iTunes Match) in iTunes > iTunes Store.
Note: You can switch the Apple ID you use for store purchases at any time. However, you can only change the account you use for any iTunes in the Cloud features once every 90 days. See this article for more information.
Using a MobileMe account with iCloud
If you have a MobileMe account (you have an email that ends in @me.com or @mac.com), you should enter your MobileMe email address when prompted for your Apple ID. This will set up MobileMe mail, contacts, calendar, and bookmarks on your device. This is also an important step for moving your MobileMe account to iCloud.
iPhone, iPad, or iPod touch:
When you first set up your iOS 5 device, enter the email address you use with MobileMe email as your Apple ID. If you skipped the setup assistant, go to Settings > Mail, Contacts, and Calendar, select MobileMe add your MobileMe account.
In Settings > Store, confirm that the Apple ID at the bottom is that one you use for store purchases. If it isnt, tap to sign out and then enter the Apple ID you use for purchases.
Mac:
Enter your MobileMe account in Apple () menu > System Preferences > MobileMe.
Enter the Apple ID you want to use for store purchases (including iTunes in the Cloud and iTunes Match) in iTunes > iTunes Store.
PC:
Enter your MobileMe account in Control Panel > Network > Internet > MobileMe.
Enter the Apple ID you want to use for store purchases (including iTunes in the Cloud and iTunes Match) in iTunes > iTunes Store.
Moving to iCloud
After setting up your devices and computers with MobileMe as indicated above, you can move your MobileMe account to iCloud. After you move, you will use your MobileMe email address for signing in to iCloud, and you will be able to access your mail, contacts, calendars, and bookmarks on the new service. Before moving, you should make sure your are running:
iOS 5 or later on all iOS devices you want to use with iCloud.
OS X Lion 10.7.2 or later on your Macs you want to use with iCloud.
Windows Vista (Service Pack 2) or Windows 7 on the PCs you want to use with iCloud.
You can move your MobileMe account to iCloud by visiting me.com/move.
Frequently Asked Questions
Can I merge multiple Apple IDs into one?
You cannot merge two or more Apple IDs into a single one. You can, however, use one Apple ID for iCloud services and another Apple ID for store purchases (including iTunes in the Cloud and iTunes Match). See Using one Apple ID for iCloud and a different Apple ID for Store Purchases above for details.
Can I change the name of my Apple ID?
Yes. For example, if you get a new email address, you can change your Apple ID from your old address to your new address. For more information, follow the steps in this article.
Note: @mac.com and @me.com Apple IDs cannot be renamed.
I have purchased music, apps, or books with multiple Apple IDs. How can I get all of this content onto my iOS device?
First, you need to copy all of your purchased content so it is on the same Mac or PC with iTunes. This computer should be the one you sync your device with. For more information on how to move your content, see these articles:
Mac: iTunes for Mac: How to copy purchases between computers
PC: iTunes for Windows: How to copy purchases between computers
Next, authorize your computer to play content with each Apple ID in iTunes. Once your computer is authorized for all your content, it can be synced to your iPhone, iPad, or iPod touch.
How do I restore an iOS device from an iCloud Backup if I use different Apple IDs for iCloud and store purchases?
When you are first prompted for your Apple ID during the restore process, enter the Apple ID you use for iCloud. After your device restarts, you will be presented with another Apple ID prompt before items from the App Store and iBookstore begin restoring. This time, sign in with the Apple ID you use for store purchases.
I have an expired @me.com email address as an Apple ID. Can I use it with iCloud and receive email at that address?
Yes, if it is an @me.com address. To use your expired MobileMe account for iCloud, follow the iCloud setup instructions and enter your expired @me.com email address as your Apple ID. Your @me.com address it will be reactivated for email when you sign up for iCloud.
Important: You will need an active email address associated with your Apple ID to set up iCloud. To add an active email address, go to appleid.apple.com, sign in with your expired @me.com email address, and add an active email address to your account.
Additional Information
For more information on Apple IDs, see Frequently Asked Questions About Apple ID.
http://support.apple.com/kb/HT4895
Summary
An Apple ID is the email address you use as a login for just about everything you do with Apple, including using iCloud to store your content, buying songs from the iTunes Store, and downloading apps from the App Store.
When you set up your iPhone, iPad, or iPod touch, you use the same Apple ID for iCloud services and purchases on the iTunes Store, App Store, and iBookstore. You can, however, use one Apple ID for iCloud services and another Apple ID for store purchases (including iTunes in the Cloud and iTunes Match). You will get all the benefits of iCloud whether you use the same Apple ID for iCloud and store purchases, or different IDs for each.
Products Affected
iCloud
For guidance on which AppleID you should use when setting up iCloud, please see the sections below that apply to you:
Using the same Apple ID for Store purchases and iCloud (recommended)
Using the same Apple ID for store purchases and iCloud is recommended for most users. To use the same ID, follow these steps:
iPhone, iPad, or iPod touch:
When you first set up your iOS 5 device, enter the Apple ID you use for iTunes in the setup screens. It will be used for store purchases and iCloud.
If you skipped the setup process, enter your Apple ID in Settings > iCloud and Settings > Store.
Mac: Enter the same Apple ID in Apple () menu > System Preferences > iCloud and in iTunes > iTunes Store.
PC: Enter the same Apple ID in Control Panel > Network and Internet > iCloud and in iTunes > iTunes Store.
Using one Apple ID for iCloud and a different Apple ID for Store Purchases
You can use different Apple IDs for iCloud and store purchases and still get all of the benefits of iCloud. Just follow these steps:
iPhone, iPad, or iPod touch:
When you first set up your iOS 5 device, enter the Apple ID you want to use with iCloud. If you skipped the setup assistant, sign in to Settings > iCloud and enter the Apple ID youd like to use with iCloud.
In Settings > Store, sign in with the Apple ID you want to use for store purchases (including iTunes in the Cloud and iTunes Match). You may need to sign out first to change the Apple ID.
Mac:
Enter the Apple ID you want to use for iCloud in Apple () menu > System Preferences > iCloud.
Enter the Apple ID you want to use for store purchases (including iTunes in the Cloud and iTunes Match) in iTunes > iTunes Store
PC:
Enter the Apple ID you want to use for iCloud in Control Panel > Network > Internet > iCloud.
Enter the Apple ID you want to use for store purchases (including iTunes in the Cloud and iTunes Match) in iTunes > iTunes Store.
Note: You can switch the Apple ID you use for store purchases at any time. However, you can only change the account you use for any iTunes in the Cloud features once every 90 days. See this article for more information.
Using a MobileMe account with iCloud
If you have a MobileMe account (you have an email that ends in @me.com or @mac.com), you should enter your MobileMe email address when prompted for your Apple ID. This will set up MobileMe mail, contacts, calendar, and bookmarks on your device. This is also an important step for moving your MobileMe account to iCloud.
iPhone, iPad, or iPod touch:
When you first set up your iOS 5 device, enter the email address you use with MobileMe email as your Apple ID. If you skipped the setup assistant, go to Settings > Mail, Contacts, and Calendar, select MobileMe add your MobileMe account.
In Settings > Store, confirm that the Apple ID at the bottom is that one you use for store purchases. If it isnt, tap to sign out and then enter the Apple ID you use for purchases.
Mac:
Enter your MobileMe account in Apple () menu > System Preferences > MobileMe.
Enter the Apple ID you want to use for store purchases (including iTunes in the Cloud and iTunes Match) in iTunes > iTunes Store.
PC:
Enter your MobileMe account in Control Panel > Network > Internet > MobileMe.
Enter the Apple ID you want to use for store purchases (including iTunes in the Cloud and iTunes Match) in iTunes > iTunes Store.
Moving to iCloud
After setting up your devices and computers with MobileMe as indicated above, you can move your MobileMe account to iCloud. After you move, you will use your MobileMe email address for signing in to iCloud, and you will be able to access your mail, contacts, calendars, and bookmarks on the new service. Before moving, you should make sure your are running:
iOS 5 or later on all iOS devices you want to use with iCloud.
OS X Lion 10.7.2 or later on your Macs you want to use with iCloud.
Windows Vista (Service Pack 2) or Windows 7 on the PCs you want to use with iCloud.
You can move your MobileMe account to iCloud by visiting me.com/move.
Frequently Asked Questions
Can I merge multiple Apple IDs into one?
You cannot merge two or more Apple IDs into a single one. You can, however, use one Apple ID for iCloud services and another Apple ID for store purchases (including iTunes in the Cloud and iTunes Match). See Using one Apple ID for iCloud and a different Apple ID for Store Purchases above for details.
Can I change the name of my Apple ID?
Yes. For example, if you get a new email address, you can change your Apple ID from your old address to your new address. For more information, follow the steps in this article.
Note: @mac.com and @me.com Apple IDs cannot be renamed.
I have purchased music, apps, or books with multiple Apple IDs. How can I get all of this content onto my iOS device?
First, you need to copy all of your purchased content so it is on the same Mac or PC with iTunes. This computer should be the one you sync your device with. For more information on how to move your content, see these articles:
Mac: iTunes for Mac: How to copy purchases between computers
PC: iTunes for Windows: How to copy purchases between computers
Next, authorize your computer to play content with each Apple ID in iTunes. Once your computer is authorized for all your content, it can be synced to your iPhone, iPad, or iPod touch.
How do I restore an iOS device from an iCloud Backup if I use different Apple IDs for iCloud and store purchases?
When you are first prompted for your Apple ID during the restore process, enter the Apple ID you use for iCloud. After your device restarts, you will be presented with another Apple ID prompt before items from the App Store and iBookstore begin restoring. This time, sign in with the Apple ID you use for store purchases.
I have an expired @me.com email address as an Apple ID. Can I use it with iCloud and receive email at that address?
Yes, if it is an @me.com address. To use your expired MobileMe account for iCloud, follow the iCloud setup instructions and enter your expired @me.com email address as your Apple ID. Your @me.com address it will be reactivated for email when you sign up for iCloud.
Important: You will need an active email address associated with your Apple ID to set up iCloud. To add an active email address, go to appleid.apple.com, sign in with your expired @me.com email address, and add an active email address to your account.
Additional Information
For more information on Apple IDs, see Frequently Asked Questions About Apple ID.
