I have been unimpressed with the in car navigation systems I have tried, mostly in rentals. Aside from the highly distracting nature of the devices, they are only as good as the data that they have. A case in point is the London, England ambulance crew that was supposed to transfer a patient to a hospital about twenty miles away. The crew, which was apparently new to the job, relied on the in-vehicle GPS system, which took them on a 200 mile trip because the data in the device was faulty. The crew was reprimanded and told to "learn to think for yourselves." Indeed.