The Wall Street Journal has some good stats on the portable navigation market. The story also offers a good overview of the features that are available in GPS units.

The U.S. market for such gadgets continues to expand: Sales of after-market personal navigation devices experienced triple-digit growth in 2006, with over 2.2 million new units sold, according to the Consumer Electronics Association. And forecasts suggest sales could surpass 3.3 million units this year.

That would, for the first time, make annual North American sales of these devices worth more than $1 billion and cement their position as one of the hottest segments in consumer electronics.

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In 2007, portable-device sales will likely outnumber sales of built in by more than two to one according to Phil Magney, president of the Telematics Research Group.

Falling prices have gone a long way toward driving demand for portable GPS devices. Average unit prices fell to $395 last year, from nearly $550 in 2003, according to the Consumer Electronics Association.