Accelerometers are one of the more interesting bits of hardware in smartphones. Earlier devices like the OpenMoko "Neo" smart phone and the Apple iPhone included them. Before Android was released I was advocating for OpenMoko at open source conferences. One of my favorite imaginary applications was private key generation. Adhering to the theory that "When privacy is outlawed, only outlaws will have privacy,", several people were talking about this as early as 2008 (when I presented the idea, to great applause, at the Ontario Linux Fest). The idea is: if you can't or don't want to exchange private keys over a public channel, you meet on a street corner and shake hands - with each hand having a cell phone concealed in the palm. The devices are touching each other, thus their sensors should record exactly the same somewhat random motions. With a bit of mathematics to filter out the leading and trailing motion of the hands moving together, both devices should have quite a few bits' worth of identical, random data that nobody else has - just what you need for crypto key exchange. I've yet to see anybody implement this, and I must admit I still hope one of our contributors will come through.
Meanwhile we have many other recipes on accelerometers and other sensors in this chapter...