Having everything on Google should be fine. Address Book will sync right to it once you get the phone, and calendars can go both directions if you use one of the sync tools out there. I'd recommend sticking to one that works with the iSync framework, that way it has a better chance of working well with the built in apps, and dealing with the iPhone <-> Mac <-> Google <-> Other Laptop situations. I've used .Mac to sync now for 6 months, and the conflict resolution in iSync works for me decently with the following setup:

Exchange <-> Entourage <-> Work Mac <-> .Mac <-> Home Mac <-> iPhone

I can plug in calendars anywhere in that chain, and iSync is what handles the conflicts for every step except the last bit between Exchange and Entourage.

The advantage MobileMe will have is that you get rid of the multi device chains of syncing, and instead put the "cloud" at the center. The iPhone pulls from the cloud over the air, the Mac pulls over the wire, and the Windows machine does the same too. Currently, there is no way to have Google just push contacts and calendars right to the iPhone, it has to go through a Mac or PC first, and be synced over USB.