Apple has finally released Mac OS X Leopard 10.5.3. Interestingly, this update adds a feature which you can sync your Address Book with Google Contacts; contact information in your Gmail account.
The catch is, however, that you need an iPhone to use this feature. I really wonder why this is the case. Technical reasons? I don't think so. Apple probably wants to sell you an iPhone if you don't have one yet, because you want to sync your Address Book with Google Contacts so bad...
And, don't get too excited. This does not sync iCal and Google Calendar. That's a third party's job.