I believe it much depends on what you use the program for. If you just edit your holiday photos for printing on your homeprinter (or at the photo-store), or make stuff like maps and the like, I'm sure GIMP is just as good as Photoshop - and personally I still miss the brush-pipe-function that GIMP has, thinking photoshop brushes really are missing the ability to have colored brushes. That being said - if you use the program for professional work, then you will probably be sorry not to have the CMYK color option when you work with GIMP - that is definitly a major reason for using photoshop (in addition to the partners you might work with might use adobe also and send you files for that.)
But if GIMP can do the work - I see no reason to spend the money on Photoshop. I sure would like to save the to many dollars I pay every 1,5 years for the program, especially since adobe charge double in Denmark than they do in the US (for the same program).
