I definitely think MobileMe is worth it.
Email: All in one place. Everything is in the cloud and it's pushed across to all of your devices. In my case, my iPhone & Mac
Contacts: I love knowing that when I put a contact in on my Mac, it's on my iPhone instantly, and vice versa.
Calendar: Again, all in one place. It's a great way to stay organized and I use it every day. What ever I put in on my iPhone is on my Mac in a second.
iDisk: Another great feature, I keep school files on there so I don't have to bring a flash drive to and from school to transfer files.
Gallery: I use it to share pictures with family, it's pretty nice.
Find my iPhone: I think this is one of the best features; if you lose your iPhone, or even misplace it in your house, you can locate it, display a message and/or play a sound for 2 minutes (even if on vibrate), remote wipe it if you've lost it for good, or remote lock it with a new passcode.
All in all, I'm glad I shelled out the $100.00 for it. It's a great service that I use subconsciously every day.