There's a good discussion going on at NewsForge related to a commentary on the use of free versus proprietary software. Should you sacrifice your software rights and beliefs if there is a proprietary software that has more features to use, for instance, in your business? It's an interesting debate. I've got The GIMP and Paint.net on my PC at home and use them fairly often in place of PhotoShop Elements, but then again, I don't rely on either program for my job.
Though it's a sidebar issue in the larger discussion, I don't think The GIMP's interface is all that bad. A friend of mine has told me that he finds it atrocious and he has gone back to using PhotoShop. I understand why Windows users might feel more comfortable with the proprietary product. On the other paw, I'm pretty utilitarian about my interfaces. As long as I understand and become comfortable with an interface, I'm happy with it and don't see a need to complain unless a competitor's product either offers more functionality or keeps the other users I deal with happier.