It was bound to happen. We can create smart groups in iTunes and iPhoto. Now we can do it in Address Book as well. The advantage, of course, is creating smart groups allows us to create email groups and add to them automatically.
In Address Book, select File > New Smart Group. Set the conditions in the same manner as for smart group designations in other Apple applications, for instance put a common identifier in the Note section of certain cards. A number of designations are built in. If you are using your Address Book for work you can create a Smart Group for everyone who works for a specific company.