Horses for courses really. GIMP is pretty powerful but it has a pretty poor user interface and you do kind of have to bludgeon it into submission a bit, but you can get some pretty impressive results way beyond the rather dismissive "resize and crop a picture" that AC@14:38 seems to think its level is at. Users who want to do that are better off with Paint.net and I active dissuade such users from using GIMP - it's way too powerful and complicated for simple tasks like that.
The main draw (no pun intended) for me is that GIMP gives you a hell of a lot and it's free and Open Source. Photoshop may be fine for those with incredibly deep pockets or very loose morals, but quite simply I have neither so GIMP is a very credibly alternative.
Sure, Photoshop users look down their nose at GIMP users, but at least we have the smug satisfaction of knowing we have both our kidneys and a clear conscience. :o)