Well, for me, I only know very basic things in using GIMP. Using curves, or basic layers to change the light or dark areas of a shot.
There are quite a few tutorials that help get these small things down that help to enhance the photo. For me, I still rely on trying to get a really good shot out of the camera first, and then do small touches to make it "pop"
There are some people on here who use just the very basic tools such as picasa to edit their photos. By all means, you do not "need" PP to get an amazing shot, rather learning about composition, lighting, and camera settings will make you progress from snapshots to art!