Exact situation but in reverse. (Windows but only because I refuse to use Mac OS and I need Photoshop.)

I tried GIMPing it under various Linux distros for a while but it's just not comparable.

That's the major stumbling block for me; slowly I'm moving towards Linux but I still need photoshop. I look forward to the day when design teams produce their work in something other than that monolithic software. Don't get me wrong, it's an amazing tool, but there's no need for anything that complex in web design.