Offering inexpensive personal satellite navigation systems for use in your car, they were a popular choice for those not willing to spend sometimes ten times the price for one integrated into your dashboard that did the job no more effectively.
The PND market appears to be tailing off a little though, and Garmin has announced an expected 8-12 percent drop in revenue this year. Rival TomTom has also projected a rather gloomy sales forecast.
Though the devices themselves are getting better and better, they're losing ground to the latest batch of smartphones that often offer GPS navigation services for free as well as offering many other features besides. More cars now allow you to hook up your smartphone to benefit from other features too, so PNDs are starting to look a little clunky and featureless in comparison.
To compensate, TomTom is attempting to diversify into traffic reports and mapping services and Garmin is putting more faith in their traditional markets of outdoor, fitness, marine and aviation markets. The company is also going to be working more closely with auto manufacturers to develop built-in devices, the cost of which is slowly beginning to decrease making them a more attractive option.
The PND market isn't dead just yet though. With basic devices starting in the $50-60 range, there will still be a market for personal in-car navigation for a good while yet.