Steven Frank of well known Mac development house "Panic" blogged about the details lost trying to sync contacts through Google instead of MobileMe:

http://stevenf.tumblr.com/post/618349003/here-are-some-thing...

His summary: "If you’re contemplating this change, I highly recommend setting aside a few hours for research first. You may be unpleasantly surprised."

Some more issues are discussed in today's TUAW article, "Sync Wars: Address Book vs. Google Contacts":

http://www.tuaw.com/2010/05/22/address-book-vs-google-contac...