We have written before about a developer figuring out how to render video from the camera on a directX surface but at the time a practical use escaped us. Baldido however soon provided an answer, in the form of this Heads-Up Display for the HTC HD2 which uses the accelerometer & compass sensor, with the live camera preview is used to fake transparency.
Can our readers think of more uses? Email and Walk for Windows Mobile maybe? Let us know your ideas below.