I have been wanting one for a few years now
Its like a lot of gadgetty things as its not needed but its fun to own.
You can link it into your mobile and then ring from the carpc, using it for router planning, have ur whole music collection on it and do stuff like that
Also if ya wanna be really geeky ya can get a webcam hooked up at the back of the car and run it through so ya can use it as aparking detector