GPS units are very overrated as of now, the signal doesn't penetrate trees very well yet, and there are too few satellites. While the SV constellation consists of 32 satellites, typically only 24 are in operation at any given time any of which could be malfunctioning. That number is enough satellites to theoretically cover the entire globe with 5 satellites something like 95% of the time. But terrain and trees often reduce the number of usable satellites to 1-2, not enough to determine a location. And the farther north you go, the worse it gets. Here in MT there are typically 20-30 minutes a day that we only have 4 satellites above the horizon, but when you throw in mountains that number is closer to an hour and if you are in a canyon, forget about it. Then if you are under a dense canopy, you will probably pull your hair out trying to acquire a satellite fix.

While a GPS can be a great tool in a survival situation, in my neck of the woods, I would rather rely on a map and compass. That isn't to say that I don't carry my GPS with me, it is a rather handy device, but I won't rely on it for survival. Now if the military would put some better satellites up there, I may change my mind.