The Kinect is an interesting device. While the fact that my Wii remains unused for 6 months at a time till a decent game comes about will show I have little interest in motion gaming. I am interested in the techs used. The Wii's original solution involved tracking via infrared sensors and accelerometers. It works but is not very accurate. They added the motion plus device which contains a gyroscope and an additional accelerometer to give it a 1:1 ratio of movement even if the infrared sensors loose sight.
The Playstation2/3 had the EyeToy and it could track motion on a 2d plane but that was it. It worked but was limited. So they added the Move which combines the same tech as the WiiMote except it uses the EyeToy camera and a color changing soft ball on the end to gage depth in the 3d space.
Kinect uses a series of cameras and infrared emitters to track you in a 3d space. It works quite well and people have already started hacking to see how it works. Kinects biggest drawback is the tech relies on how far away you are from the rig. If you're not in the sweet spot tracking isn't as good.
I think the Move is probably the most accurate of them all but as I've always said if it doesn't all come in the box with the system then it's doomed to fail. Software developers want to sell tons of games. Making a game for something that not everyone has limits your sales and your budget. Good games will be scares and most likely for the Move it will be for half a$$ed tacked on features to other games. We'll have to see how they sell. At least Nintendo started packing the Motion Plus tech into New Wiimotes now.
Here's a cool video of what the Kinect is acctually doing.