http://kinectmidicontroller.codeplex.com/
 
I thought this was a fun project. It isn't very tricky. There's a nice video of how you can use your Kinect sensor for your Xbox to control your synths.
 
:-)
 
Total diversion but kinda fun.

Cool. I want to try it!

Ooooh, virtual theramin

this is one of those things that i'm dying to delve into. right now i'm playing around with using pure data and webcam arrays to trigger midi events and algorithms, but kinect integration looks like a blast.  this guy chris vik has an awesome piece of freeware for the kinect sdk - here's an example of how it works. pretty awesome.  http://www.youtube.com/watch?v=qXnLxi2nzrY&list=UUAaWyl3kfnCJ3nnqrQ53Q-w&index=6 

Heads up, I had to buy an adapter to plug in my Kinect to my PC. The adapter comes with a plug for the wall to power the Kinect as well as standard USB plug.
 
http://www.amazon.com/Xbox-360-Kinect-Adapter-Power-Supply/dp/B004IXRXGY/ref=sr_1_1?ie=UTF8&qid=1308269162&sr=8-1

They also sell a cool thing to make it so you can use your xbox controller with the PC (which I also have). My kid and I use the xbox Kinect and controller to control our NXT 2.0 robot which is fun.

We can then write our own c++ or c# apps to receive input from our controllers and send directions to the robot over Bluetooth

I haven't actually taken the time to use my Kinect as a midi controller, but I thought it was fun that someone wrote it.