I use a great add-on tool called Thunderplunger to clean up my address book in the Mozilla Thunderbird email client, but I need something similar for the original Mac Address Book too. Basically I have big email lists of subscribers from the last few years. By the time they got removed though and I get a lot of bounces when I try sending newsletters (which they opted-in to!), but it's too tedious to delete them one by one, especially when I want to send a newsletter after some time has passed and many mail addresses changed/got deleted.
I know there's no 100% method to filter out invalid addresses, but it helps at least a bit. If there was a method to import/export addresses and all their information (I have some special fields like categories and notes) from Address Book to Thunderbird and the other way round - that would solve the problem as well. But I can't believe there's no tool out there too clean up your Address Book ?!