With Google Maps Plugins (from Brian Toth) you can easily extend your Addressbook on your Mac. When you download the ZIP Archive you can install it with a double click.
When successfully installed the Addressbook gets new menu entries on its right click menu. The aditional menu options are seen only when you are NOT in "edit" mode of the Addressbook entry.
By clicking the Google Maps Preferences you can easily set up which contact information should be shown.
Google Adressbook with Mac OS X Adressbook sync:
With the version 10.5.3 and above it is very easy to sync yout Mac OS X Addressbook with Goolge Addressbook. Aditionally you can add the Addressbook of your iPhone to the account. To do this go to Addressbook> Preferences > General and check the box sync With Google. Then just add your credentioals and click "OK".