Heh, I used to use bluetooth GPS tracker with my nokia 770. It worked well since I could place the gps where it got the best signal. I could start a track, have it record it, and then check in with the n770 only when I needed to see a map. That way I made the most of my n770's battery life, but still got continuous tracking.
Beware that they take much longer to start since they don't know the GPS coords of the nearest cell tower, nor do they download the GPS almanac over the cell connection. They will however remember the almanac so you can leave it on for 30 minutes and not have to redownload it the next day.