As for the GIMP, as far as I'm concerned professionals will just consider it a toy to play with. The marketing/image does them no favours (a cartoon character and a silly-sounding name), and the interface is a PITA (it takes several keystrokes/commands to do what would take one in Photoshop).
I'm always in favor of open source solutions, but GIMP is sadly not even in the same league as Photoshop. It's getting to be a fairly competent photo editor (although my understanding is that it has quite a ways to go still in terms of color management), but its design tools still lag horribly -- comparable to something in the Photoshop 4-6 range, which I suppose is usable, but wastes so much time doing simple things that a serious pro would be better off just buying PS. It would pay for itself in a week or two.