If you edit a card in Address Book, and double-click on the icon well, you now get a nice dialog to set the icon, instead of just a File Open dialog. It's much like the iChat icon dialog, in that it lets you zoom and crop the picture. Also, if you have a camera attached, you can take a snapshot from the camera and use that.

If you do this for youself, the picture becomes your login picture as well. With the snapshot feature, it's easy to take a quick snap of everyone in your family, and when you get mail from them, their picture shows up in the Mail header also. Pretty neat.