First, Faces offers Address Book contacts as potential matches for unrecognized faces (based on initial letter), each labeled with an Address Book icon. Formerly, you'd be presented with the names of previously identified faces only.
Also, the label that identifies an unknown face has been changed from "unknown face" to "unidentified."
This one could be just in my head, but zooming in on the Places map with a double-click seems a lot faster now.
They're minor changes, but definitely welcome. Many people dismiss iPhoto, but as a snapshot professional, I love it.