Prosopagnosia

Prosopagnosia transfers contact information from your address book and into your iPhoto Faces. It currently supports Apple Address Book, Gmail, Mozilla Thunderbird and Microsoft Entourage.
Having your contact information stored in iPhoto as well enables you to upload your images to Facebook without manually having to tag your iPhoto Faces with full name and email address.

Just use first name or nickname when tagging your contacts, and Prosopagnosia will automatically find matching contacts in your address book.