With sales skyrocketing in the past year, GPS-based navigation systems are one of the hottest accessories (or necessities) for new vehicles. Apparently lots of car buyers like a disembodied voice directing them to unknown locations, while watching a display of their progress.

But your navigation system is only as good as the information in it. Marty Callner discovered this the hard way when he followed his Mercedes-Benz SL500R's navigation system's advice - following a detour which ultimately stranded him in the middle of the desert with a flat tire.

And it's getting worse. Cities, highway, and street systems are getting larger and more complex, often more quickly than your navigation system's database gets updated. And then there's the navigation software - most major automakers have issued service bulletins fixing everything from locked out displays to calculating routes parallel to (but not using) the correct roadways.

A reply to Mr. Callner’s attorney said it best: "We must remind you (and your client) that a GPS system is not meant to replace regular maps, or driver judgment, but is simply an enhancement to travel available to vehicle operators, which they may elect to use or not. A driver uses a navigation system at his or her own discretion."

[Thanks, Cary!]