I think the worst problem with GIMP is not that it isn't a powerful enough tool, but that they make it a point of the project to make it as distinct as possible from photoshop, so a lot of pros don't really want to even bother learning how to use it. I have tried using it a few times in place of my pirated copy of Photoshop (whenever it stops working), and everytime I try, it baffles me how making something that is obvious and intuitive in photoshop needs 5x more work to do it in GIMP.