I started using this free software on my mac called iLovePhotos. It makes it easy to tag the people in my photos, its really cool! One thing it does automatically is assign tagged people in my photos to my contacts, so I really like the integration with the address book. This in turn affects my contacts on the iPhone: Imagine my surprise when I get a call from Maria, my fiancee, and her picture comes up, without me putting it there! Nice surprise.