The Kinect can track people in 3D space due to its ability to see depth.
The parts of the Kinect that interest me are the infrared projector and infrared camera.
The projector projects an array of dots that the camera analises, returning a grey scale image based on the density of the dots (more dense for close objects less dense for further away objects).
So why is this exciting ?
Firstly its exciting because it reduces many of the problems with traditional motion tracking based on a standard camera.
As it uses depth not light its easy to remove any background imagery, just remove anything darker than you are interested in.You can can also use it in poor lighting conditions (making it much more suited to gallery or theatre applications).
This first point makes it interesting in that it opens up many previous ideas that had been mothballed due to lighting and object extraction issues.
The main thing however that has me excited is idea that this device offers a new way of seeing.