The Mobile Technologies Group (MTG) at Georgia Institute of Technology developed a technology to detect motion via the camera.
This works through motion blur detection and optical flow, and enables detection for up to 6 degrees of freedom.
They have developed a pong where the user moves the phone back and forth to control the paddle, a doodle game to show off the degrees of motion, and multiplayer pong via Bluetooth
Sounds to me like they're pretty much able to mimic an accelerometer / tilt sensor.. which can be a controller for hundreds of games or apps.