I’ve been using Gimp for many years on many OSs. On Mac OS X it feels clunky though. Spreading its UI across several autonomous windows means you have to “nearly, but not quite” double-click everytime you want to change tools or tweak something else with your mouse. That is, unless you change the above X11 preferences 🙂
The “Click-through Inactive Windows” is pretty much mandatory for my typical Gimp usage. The “Focus Follows Mouse” is just added sugar for people missing auto-focus on Mac OS X, at least with X11.
Add to that a neat and thoroughly put together Gimp Distribution for Mac OS X, and I’m in heaven 🙂