GPS units are becoming cheaper and cheaper, which means more than saving a hundred bucks on a Christmas present. Since GPS units are essentially just receivers that can do math (to triangulate your position, basically), when the chips' cost falls that's a big share of the cost of the unit.
But what happens when the chips move out of the GPS units and into cell phones (obvious applications), cameras (Flickr geo-tagged pics), and of course advertising. Business Week points out that a company named Yell.com is putting GPS-enabled ads on the sides of London buses. This lets them serve ads based on where they are.
Look for 2008 to be the year that we started to see GPS technology really change our lives as it moves out of the car and into a lot of unusual places. The marketing implications are huge.