Gimp 2.8.0 is available for Mac OS X now.
You need to have XQuartz installed on your Mac for the new Gimp version.
Why should you upgrade to Gimp 2.8 ? For me there is one major change I am waiting for years now. The one window mode. Gimp uses X11 and on Mac OS X the multi window tool boxes don’t have a good useability.
If you want to have the one-window-mode your default mode. Open Gimp got to Windows -> Single-Window Mode.