Good riddance to a terrible service. Honestly, how can Apple justify £59.00 per year for this nonsense?
The service is advertised with the promise of "Exchange for the rest of us" but from my two days testing it there was nothing of the sort. The promised "Push" for my data did not happen in any direction between any of my devices.
For example, one would expect that by "Push contacts" Apple meant that as soon as you updated a contact's card or added a new one on your Mac it would send it up to Mobile Me and to your other computers and phone. The "Automatic" syncing option in the MobileMe area of System Preferences seemed only to perform periodic syncs which were in no way influenced by my activity on the computer. When I changed a contact's card it didn't reflect instantly on my iPhone and before I cancelled my account I was still waiting for an update to my contacts to be delivered to my iPhone to reflect changes I made on the computer (and manually synced) three hours prior.
Email was no better. I could send an email from my Gmail account to my Me.com address and not see it spring up on either my computer or my phone unless I did a hard refresh. iPhoto didn't manage to connect to what it thought was still .Mac, so there went my chance of trying out the web galleries feature.
It became apparent that Apple's definition of "Push" is merely more frequent refreshes of data, and to me this isn't doing any better than Gmail. The web apps were slow and buggy on my 2.4GHz iMac and Safari would hang when I moved contacts between groups on the Contacts application online.
Things which I did like were the syncing of my Keychain, Dock and System Preferences, but unfortunately if you chose a nonstandard desktop wallpaper it wouldn't transfer that to your other computer. These last features are promising and there really is no reason why they couldn't allow people to sync that data via FTP to their own webspace, but I guess they would lose out on revenue then.