Are you under the assumption that OS X can't be changed? 'Cause with plists etc, you can do a great deal...
Unfortunately, neither Illustrator or Photoshop are available on Linux. Are their open-source equivalents anywhere near the quality of their Adobe counterparts yet? I've yet to try InkScape, but I know that the last time I used Gimp, it was excruciating. I would rather work via ImageMagick, RMagick or node-canvas than subject myself to gimp.
https://launchpad.net/pipelight
or (older)
It's the standard F/OSS model of "open source replacement for commercial software" that has some list of features nobody but nerds cares about and is completely unusable for day to day work. It's sad.
Surprised someone hasn't made a LOGO-like language for raster editing.
Is there any specific motivation to switch to linux? OSX might not be libre, but it mostly works (apart from setrlimit).
To be fair, it's a LOT better since they added the single window mode. I've been using it since then and I am quite satisfied (although I am not a heavy user). Maybe you should give it a more serious try. Inkscape is also pretty good I think.
[1]http://elementaryforum.org/forum/how-to/customization_aa/des...