I can think of many things you could do with this... generate graphs both on-screen on the empeg and in html format that can be viewed in the car via hijack's khttpd. But I'm left wondering how accurate something plugged in via serial can be.

I don't know much about GPS data, but some of the samples that people have posted appear to be on the order of 100 bytes. At a baud rate of 9600, that only allows for 96 updates per second. If it clogged the serial port by transmitting bits in a continuous stream without any gaps at all, you'd only be able to get resolution to the 1/100th of a second. That would be good enough, but the question is: does the GPS really send 100 updates per second?

Either way, it'd still be good for a trip computer... total distance, total time stopped, average speed and with a little bit of data (geographic borders) states (or countries) visited, when there and for how long; distance to destination, estimated time remaining. When you get gas, if you tell it how much you get, it could tell you average MPG for the last tank and plot that versus average MPH for that tank.