Santa put a Garmin Nuvi in my stocking. Quoting from the front page of the "Important Safety and Product Information" instructions included with the unit:

Failure to avoid the following potentially hazardous situations could result in an accident or collision resulting in death or serious injury.
...
When navigating, carefully compare information displayed on the unit to all available navigation sources, including information from street signs, visual sightings, and maps. For safety, always resolve any discrepancies or questions before continuing navigation and defer to posted road signs.
...
Always operate the vehicle ina safe manner. Do not become distracted by the unit while driving, and always be fully aware of all driving conditions.
...
The unit is designed to provide route suggestions. It is not designed to replace the need for driver attentiveness regarding road closures or road conditions, traffic congestion, weather conditions, or other factors that may affect safety while driving.
(emphasis is theirs)

This sounded like "common sense" to me. Apparently not.