Here are the OS X Address Book "General Preferences" on my 10.5.7 MacBook (where I sync my iPhone):
And here are the same settings on my 10.5.6 iMac
Right. The 10.5.6 iMac has an option called "Synchronize with Google".
How the #$! did that get there? Why doesn't the MacBook have this option? (By the way, Google Apps Exchange Sync still doesn't work in 10.5.7).
Lifehacker has the answer. Turns out this is quite old (I even sort of remember reading about it):
Mac OS X Leopard only: Today's release of Mac OS 10.5.3 added a juicy little tidbit to Address Book: the ability to automatically sync your Google contacts. After you've run Software Update and gotten 10.5.3 (and restarted your Mac), hit up Address Book's Preferences pane. At the button of the General tab, check off the "Synchronize with Google" box to get started. Be sure to back up your address book before you sync, and see the FAQ for more info. Update: Several commenters rightly point out that this capability only exists for iPhone and iPod touch owners by default, which is quite possibly a crappier move than forcing Safari onto Windows users on Apple's part. Time to switch to Linux. Update #2: Only a few hours later, a workaround surfaces. Non-iPhone/iPod touch owners, here's how to enable Google Contact sync.Alas, I read through the comments on the hack to enable Google Contact sync without an iPhone/iTouch and it sounds problematic.
Based on a similar story with Exchange Sync this feels like a side-effect of iPhone synchronization. It's obviously disappointing that none of this stuff improved with 10.5.7. I'll take a look at the Google sync, fortunately it's easy to restore contacts. I'll just make sure I turn off MobileMe sync before I experiment.