Of course I bought my TrackIR (3 with vector expansion) for playing some simulators, but i recently discovered that you can nicely utilizise it in windows too!
While its actually not precise enough to use it as a mouse - its sooo nice, wenn you map it on the arrow keys and use it to scroll through eBooks with just nodding your head for a bit! Its actualy easier than reading a real Book, which you have to hold in your hands and switch pages occasualy!