How do I sync GMail contacts into my Mac?
If you are using Mac OS X 10.5 or later, it's just a matter of enabling in in your Address Book:
On most modern Macs (Mac OS X 10.6 Snow Leopard) you simply open the Address Book (-,), click on Accounts tab, and then under the left column, select "On My Mac (Local)".
Then click on the "Synchronize with Google" checkbox and enter your Google credentials, and voila! note that synchronising may have deleterious effects because of inherent problems with most sync systems. To be safe, I would back up either (or both) your Gmail and Address Book contants before proceeding.
To back-up your Address Book contacts go to File menu > Export… > Address Book Archive…
Your Gmail contacts can be backed up in this way.