GPS is a great thing. You can do waypoints on sign throught the woods that you would never find again. And if it gets dark, that GPS can mean the difference between finding the car, or sleeping out under the stars.
But I have had them fail. I have had them give bearings that were off as much as 90 degrees. I have gone whole stretches of woods where the mountains screwed up too many of the satellites for it to work properly.
Basically you need a map, at least one compass (and I would agree with more), a flash light, and at least 3 ways to start some fire. Whenever people see me in the deeper woods, they always laugh because I am carrying enough gear to easily make it thru the night if I have to.
When you are wandering around the woods, it is not the gps you are watching, it should be your compass and map. I use the gps really only as a 2nd check on where I am, or how far I have to go to get to a point. That way, if the gps gets smashed in a fall, I pretty much know what direction to go in to bushwack out to the car.