This tip comes in quite handy when you find yourself managing multiple address book groups that start to overlap. For instance, my address book contains groups for the Macgasm team, the iPhone reviewers, and the editor team. Some contacts are in more than one group, but it’s hard to remember just what groups they belong to at any given moment.
The fix is quite simple–select a contact you want to track down, and then hold down the option key. The groups will light up where your contact is residing.