This offered up by Mark at Village Voice:

face recognition (and priority)

Joe that works for free shots with lots of faces, and works very well. But it does more : if you press the joystick on the box/face that you want then the box with the face in it is locked (the color of the box becomes red) and the camera starts tracking. But the other faces will stay boxed (white) while tracking the red one only. Press the joystick again and the red one is unlocked. And you can go from box to box and lock the one that you need if you want to track that one only. With lots of faces (and white boxes) and none locked (red) then the camera decides based on priority. This is by far the best tracking system that I had the pleasure to work with in YEARS.