The latest GIMP update (2.8.2) for Mac is pretty significant in that it no longer runs under x11. This means that it is completely standalone and that above all it will work in Mountain Lion, where X11 support has been dropped, MacGeneration reports.
The update also includes a ton of bug fixes and optimisations, the full list can be viewed here. The app hasn’t yet been certified by Gatekeeper, but that will almost surely come in due course.
While X11 support has been dropped on Mountain Lion, it does have a replacement in XQuartz. However the GIMP developers clearly thought that making it a standalone app was a good idea, and I couldn’t agree more.