I joined Mobile Me (.Mac) in 2003 and haven't looked back.
What I like:
1. Amazing SPAM filtering (less than 25 SPAM emails since 2003)
2. Keychain sync between my 3 Macs
3. Calendar sync between my iPhone / Mac
4. Bookmark sync between my iPhone / Mac
5. Preferences sync between my 3 Macs
6. Secure iChats
7. Disposable email aliases
8. Find my iPhone / Remote wipe (could be very handy)
What I don't like:
1. iDisk whenever I have used is painfully slow and unreliable
2. iPhoto album publish is slow and unreliable
3. Price
Just my opinion and I intend to pay again this year if it's not free, if it is free I hope they maintain the good points and improve the bad points.
mrzippy you bring up a great point. I've only got one Mac so my sync is generally going to my iPhone and iPad. If you've got a couple of Macs then
Keychain sync
Pref sync
Dock items sync
Would be a godsend. In fact I am getting a second Mac soon and thus I will enable those features to be sync'd.