I know I'm going to get in trouble in some quarters for saying this, but GIMP is a perfect example of what, as a Mac user, I am NOT looking for. It's ugly, it's not fully functional, it's still not up to snuff after what, 20 years of development?
Sure its free, but if price were my primary concern wouldn't I be using Linux or Windows?
I'm a Mac user. I want professional-grade, high-quality apps that are highly functional and highly elegant, with a strong sense of UI and a low chance of problems. It doesn't have to be perfect, but it does have to exude quality and craftsmanship.
Call me when you find a print shop or publisher that's thrown out Photoshop in favour of GIMP. Nuff said.