Now I'm just a newbe to Android, but I have the Garminfone and it's just what I was looking for. I came over from Blackberry and I'm very impressed with the Droid platform. Granted, the fone lacks froyo and at 600mhz, it is only a matter of time before it's out of date, but aren't they all? What sold me was obviously the navigation, but it has the windshield mount and charges when snapped in (which is nice because I have noticed that the battery life is fairly short.) For my job, I needed a good gps and a good phone...got both of these (for free during the father's day special at T-Mobile) and I couldn't be more satisfied. I haven't found any real downsides to the fone yet...maybe the lack of camera flash, but I don't really use the camera anyway.
I know i'm in the minority with the fone, and I don't have any other Droid experience to compare it to, but damn this thing rocks!