I have Linux on one of my computers, and Gimp came pre-installed. I think, if you're using Linux, Gimp is great.
There is a hack for Gimp called GimpShop that I've just tried tonight
http://www.gimpshop.com/download.shtmlIt makes Gimp much more like Photoshop. I tried opening one of my multi-layered psd files, and GimpShop handled it perfectly. It even works with my tablet, with pressure sensitive response. So, get GimpShop if you're trying Gimp.
How reliable it is, I can't say... I'm still testing it. Since most of my work goes on to others who use them in print, file compatibility is important... so, I'm checking it all out. But so far, it's working perfectly.