Remember the movie "Face-Off"? This is a lot like that, but digital, and involving way more Kinect cameras.
Matthias Niessner's video is as dry as a technical paper (because that's what it is, it's his video demonstration for SIGGRAPH), but the new technology he's introducing is truly amazing. By using real-time 3D modeling and facial capturing, one actor's performance and expressions are photorealistically overlayed over another person's normal mug.
The applications are dizzying for example you could: