As I have discussed in previous posts, there are lots of great sensors at the disposal of the Windows Phone application developer. One of them is the Accelerometer. The accelerometer measures the tilt of the device in both the X axis and Y axis.
You can read my previous article about the Accelerometer in more detail.
This can be quite useful for game scenarios. It can also be useful in productivity applications where the developer is using additional forms of user interaction to offer greater usability or innovation.