Cool stuff, but I have my doubts about the usability of such technology as a gun controller. This is essentially the reverse form of the LCD Top Gun, only with this, the system is attempting to track a much smaller object.
It would also be necessary to be able to discern very minute changes in the angle of a device in the "Z" axis, which is tougher than tracking a steering control (X and Y). It may be possible with a special, and not very realistic looking "gun". At minimum, it would probably need "wings", both horizontally and vertically, and track the distances between the mapped objects on the ends. And a low-res web cam is going to provide for lousy accuracy.
RandyT