

Don’t try to do client work bound to a deadline on gimp. Because the stress will make you close gimp at the simplest inconvenience. That’s what happened to me. But trying to work with it on my free time. And installing the photogimp addon helped alot. Gimp still has a long way to go.
My comment wasn’t about specifically using gimp on Linux and dumping Mac and windows. But just about how to getting used to gimp in general.
Linux is still lacking many other professional grade software so even you find a PS replacement on linux. Other software problems might pop up.