LifeHacker suggests a method for keeping your Contacts and Addresses in Sync using the new 10.5.3 Address Book settings only. Apple added this functionality so that iPhones could sync up with Google, but it may be possible to spoof the software by editing plists and running sync against another device or against .mac
The comments don’t provide a foolproof algorithm yet, but it seems doable.
Mac OS X Leopard: Enable Google Contact Sync Without an iPhone or iPod Touch
If you don’t have an iPhone or iPod touch and unlocking this useful bit of functionality isn’t worth paying hundreds of dollars for the device, a simple system tweak can turn it on for you.
Here’s a hint from some email I received outside the blogosphere …
“The trick is that you (edit) an entry for an ipod that you no longer have (or make one up) so when you sync that (bogus) ipod it does not overwrite the entry in the prefs file when you … sync your (current) ipod.
[...] Book and GMail Contacts. Holiday cards need to be addressed, after all. We’ve mentioned sync between these two before (for Mac OS X 10.5.3+ only), but didn’t get very far before running into trouble - the Scotsman does not have a [...]