I've been skimming through this thread and decided to put in my two cents lol. I currently use the new iMAC 24in and running OSX Leopard plus CS3. In the past, I used to be a dual user with Gimp as well. Around here, I'm know for my c4d style sigs and achieved positive results on both programs. On top of that, I'm also known for making vid tuts for end users on sig creations for both PS and Gimp. I've been a PS user for centuries and since there were end users who only have Gimp, I decided to cross over and help them out. I proved to everyone you can achieve similar effects in both programs.
Granted that my forte is not in Gimp, but learned it in a couple of minutes in how to utilize basic functions. Once you get up and running, it's like Photoshop. Of course it's not mainstream or anything, but it will get the job done none the less. Although I have to admit that Gimp does have better functionality in brushing and their brush packs are better as well. Below you'll find some of my Gimp work:
At the time I was learning Gimp, I wanted to see if I can output the same kinds of results in Gimp that I can do in PS. As it turns out by looking at these raw sigs, I can output similar results. I'm actually quite impressed with Gimp after giving it a chance.
Honestly, it comes down to the end user and their preference. There's no right or wrong with either depending on what you want to do. I wouldn't write off that Gimp sucks because it's not famous as PS or because it's free... I thank the development team who created Gimp in order for those who wanted a chance to join the gfx world. I'm a PS user to heart but I can't ignore the fact that I do like Gimp as well.