This looks really cool! Are you going to set up a server to combine maps, so people can collaborate on covering large areas and getting all the roads?
I used gpsdrive on my last trip (cross country, Phoenix to Baltimore. I saved the tracks, if anybody wants them.) My impression was it was too slow on my old P133 toughbook, and the GPS kept dropping offline too; not sure how much of that was due to the cable (brand new, but wiggling the serial end seemed to help sometimes) and how much due to bugs in gpsd or something. I bet yours is much faster if you're using vector graphics rather than so much image processing.
A richer coworker was having fun with his "mechanical lady", one of those talking all-in-one GPS units with a nice color screen, maps, a database of businesses etc., and the ability to give directions. Maybe we'll get there someday.