Native GIMP....
Here is a screenshot of the native version of The GIMP I compiled yesterday. I still haven't gotten the quartz GTK theme engine to compile yet so I'm just using a custom GTK theme I edited but it's working. I have already noticed a few benefits of the native version over the X11 version. Since it's running directly in the OS X environment the mouse works better.. the scrollball on my Mighty Mouse works for scrolling in any direction and in the X11 version you could only scroll up and down. The keyboard shortcuts are now consistent with the rest of the OS like for example, command+s now saves rather than control+s. Also in general the windows behave more like OS X windows even without native aqua controls in them.
There's only a few caveats with the version I am using right now though. One of course is how I haven't gotten the quartz theme engine compiled yet. I also don't have it in a gimp.app skeleton so I have to launch it from a terminal window and keep it open to keep The GIMP open. Also dragging and dropping to the dock icon or the toolbox doesn't yet open the image. But it's a nice preview and I of course will be trying to figure out how to make it better getting the native theme to work and such.