I just got the update to 2.1 a few weeks ago and the problem just started for me. I got in the car today and turned on the view map. I live in Northern VA, it had me running through the woods north of Dublin Ireland. I tried restarting, removing the battery, that just put me in Cleveland and then it stopped detecting GPS at all.
Later I started playing with the app task killer and found that if I killed the car dock mode that it would find me right away. If I put it back in the car dock I would wind up in Michigan or Connecticut.
I took it out of the car dock and killed the car dock app again, it was fine for a while. Then once I put it in the car dock it did it again.
It's frustrating because I do need the car dock to see the screen well. I also have a Mini Cooper with a really stiff suspension. I don't know if all that rattling around is causing part of the issue but I've had the phone a few months now and this is the first time it happened. It really seems like a bug.