Here's another neat idea, guessing device-orientation based on outdoor-shadow direction, the accelerometer, and time of day. If could be a very useful function in the absence of a compass. Perhaps not real-time, but still very useful in conjunction with GPS!

Additionally, a library like this may be useful for robots that use the N900 at its core, to process visual information. Of course, the plugins would have to be fast enough to be used in real-time!

}:^)~