One of the things I'm working on involves adding a magnetometer (HMC5843 - http://talk.maemo.org/showthread.php...739#post450739) to my stack with a Venus 10Hz GPS (with WAAS and AGPS!), reading J1850 from my harley, my radar detector. I'm also adding baro and temp (and maybe humidity if I can find the right sensor).

The HMC is more than sensitive enough to give a heading reading - I was surprised. It is I2C so just needs to be turned into serial for bluetooth.