Just did a test run through my neighborhood with a bluetooth GPS and my jail-broken iPad I. Used a GlobalSat BT-368i GPS, with BTstack running on the iPad. Very, very impressed. Used MotionX HD for the mapping software. It tracked my route through my neighborhood perfectly -- even accurately gauging my Jeep was on an alleyway next to a major road, and not on the road itself. Pretty nifty, since I've never had proper GPS before.
Big thing -- I've noticed that for small/unpaved roads, Google won't load maps correctly for them. There's a public road, that's only open through certain hours of the day, but Google won't keep route information in it once you export it to a new device. Turns the squiggly little road in to a "as the crow flies" path. Bummer. Not that big of a deal, so long as you use waypoints on the device and don't forget where you're going.