Future Interfaces Group at CMU has done a lot of interesting research where they can infer a large amount of enviromental context just from accelerometer/gyroscope alone. http://www.figlab.com/

Some examples:

https://www.youtube.com/watch?v=a-ImMjOrbbI

https://www.youtube.com/watch?v=gCA-0cPS1eM

They also have a bunch of research using other sensors in the phone as an input.