This video shows an example of what can be done with Skeltrack and GFreenect.
It gets the user's head and hands' positions from Skeltrack and interprets them in order to map some gestures with events in the desktop using Xlib with the GNOME 3 desktop.

It allows to move the mouse pointer, click and drag things and it also controls the zoom level by using both hands as a pinch gesture. The video also shows how Skeltrack can be used to play video games with both hands simulating a steering wheel.

This demo application is published under GPL and you can find its code at:
github.com/joaquimrocha/Skeltrack-Desktop-Control