From that thread I learned that OS X 10.5 Contacts, astonishingly, has its own private abilities to sync with Google Contacts, Yahoo Contacts and ... Exchange Server.
Huh? Why Address Book and not, say, Calendar?!
Naturally, a fellow maniac is now using Google's iPhone oriented ActiveSync service to sync their OS X Address Book to Google ...
Google Sync iPhone = Mac OS X Address Book orphaned - Google Mobile HelpHoly Cow. I'm seriously tempted to try this. The catch is it's easy to backup and restore my OS X Address book, but it's very hard to restore my Google Contacts -- particularly their Group memberships.
1) Go to your Address Book preferences, General Tab.
2) Then check the Exchange box and click on the Exchange button.
3) Enter your Google Apps username (first part e-mail in the E-mail field.
4) The password in the password field.
5) In the Outlook Web Access Server field, enter http://www.google.com/a/yourgoogleappsdomain.com.
6) Check the sync every hour box...
Update: See Joe's comment below. I found similar comments elsewhere. This doesn't work with Google's version of Active Sync.
Update 7/1/09: Wade has an interesting comment. I may try this again with the current OS release but I'm also waiting for the new release of Spanning Sync 3 and its implementation of the Google 3.0 API.