I just installed Mountain Lion on my MacBook but I couldn’t work out how to set up synchronisation of the contacts stored on my Google account as this seemed to be left out of the Google synchronisation options:
I tried adding an exchange account in the same way you achieve push email and contact synchronisation from Google on the iPhone, but there didn’t seem to be an option to enable SSL so this didn’t work (fix this Apple!).
Finally I opened up the Contacts application and went to the account settings and there (somewhat randomly in my opinion), under the “On My Mac” account, is an option to sync with Google.
Seems Apple don’t really want you syncing your contacts with Google.