OBD-II is something I've been thinking about for a while. I've not done anything about it, but eventually I'd like to. From all the threads discussing it so far, there's a number of obstacles that need to be overcome:

1) Only one serial port and many people want GPS, OBD-II, remote display, etc
2) Software to interpret the data
3) Disk space to log to.

Here's the approaches I've been considering:

1) I've been keeping my eye out (as opposed to actively searching) for a terminal server that we could use with the empeg. The problem is that most give binary drivers for major unix distros, not linux-arm, nor do they give source code to their drivers. In another thread, there was talk about a termserv that you could program in java (IIRC, it was called TINI). I don't have the skills to program drivers for it and finding someone with the skills, time and motivation hasn't happened yet.

2) Start with some of the OSS linked in this thread

3) The best approach I can think of is to re-partition your drive (1G should be overkill) and make the new partition ext3 so it can be more safely mounted read-write in the car.

If you're not using the serial port yet, there's enough pieces available to start putting the puzzle together. How much useful data you'll be able to extract is still in question though.