The secret is in the "Categories" function of the address book, and you'll need to adopt the Categories system for this hint to be useful.
Double-click an entry in your address book. If you've never categorized them before, you'll find they're in a "Temporary" category. When you decide to keep someone, assign them to a non-temporary category.
Now all you have to do is periodically view your address book by "Temporary." If there's anyone you want to keep, assign them to a different category. Otherwise, just hit Cmd-A and hit Delete all the deadbeats at once.

