I had one case coming back from the Midwest where there was a construction detour that the machine obviously wouldn't have known about, and I had to cut about fifty miles along another route. The machine spent half an hour indicating a U-turn at every opportunity until it finally gave up and accepted the alternate route.
I would like to see more "real time" updating capacity in these things so that stuff like local traffic conditions, weather, and temporary construction situations could be fed into a centralized database and fed into a memory bank in the machine over satellite radio or cell phone networks. Right now, it's all about the DVD in there, and that gets updated only once every few years. I routinely drive an interchange overfly that didn't exist when this DVD was written, and the frantic navigator pops "bread crumbs" along a route it thinks is going through mid-air.