Darn you posted it before I did.
http://www.psxextreme.com/ps3-news/2654.html
PS3 head tracking based on facial recognition, so without IR glasses adding cost.
Additionally it seems to be able to track separate faces.
So technically you could have a split screen 3D display.
The only danger in head-to-head competition is that it could quite literal become head-to-head in your living room.
Something of note about the IR glasses.
It would requite a lot less processing load to use the IR solution.
Additionally if instead of just two temple points, they should use two temple and two brows.
Why?
Because the arced frame would allow more accurate tracking or nodding, distance, and head turning.
The Playstation Eye 2 would also allow for simultaneous physical and vocal interaction.
In the distant future people using HOME could have facial avaters.
Similar to the cartoon, Bruno the Kid.
Where your face and voice are copied and changed to match an avatar.
Video/Voice chatting and in game co-op could be dramatically altered by this.