Very interesting. I'd be nervous about Google decimating my carefully constructed contact list, and there doesn't appear to be any way to sync calendars without syncing contacts.

Still, I could back up my contacts, give it a try, and see whether the resulting contact list is over-polluted with Gmail's auto-saved emails, or whether something reasonable happens.

(Methinks I should wait for other people to try it first and see how loud the screams are.)