MobileMe is a new set of Apple web applications available for your consumption. It does a lot of things for $8.25 a month. If you're not a Mac user, it's probably not even worth checking it out.
If you are a Mac user, it's the new version of .mac.
1. Google's less pretty version(s) is (are) free. I guess you get what you pay for... MobileMe's usability and ease of interface is about ten times better.
2. The sync'ing features are not worth much for a non-iPhone user, such as me. (I don't even have my own mobile phone, so I'm not much of a market for such features. I used to be a Palm user, back in the day. But for my home-office setup, such devices don't do me much good.)
Update: Apple has experienced a bunch of problems with the service, so if you're thinking of doing it, maybe wait a month or three till you sign up.