I've used Gimp for a long time back when I did my art by mouse and let me tell you, it was great. Well, Gimp doesn't support the Surface and I -think- it doesn't support the Intuos, but I'll have to check it out later on my PC. I really miss a lot of it's features. I love ClipStudio, that's my baby, but damn if it doesn't have some of the things Gimpy does. I love using multiple programs for a picture. It's how I used to draw back when I had PS. I'd hop between it and Gimp and SAI. I don't mess with SAI much anymore since I got more comfortable with my lineart...

Anyway, I miss Gimp. It's the poor man's PS.