I'm running the PortableApps version of GIMP 2.6.11
under Windows 7 64-bit. Whenever I run it I will always get an incompatibility message about some .DLLs. I bravely forge ahead regardless and, lo!, it works fine. There are some issues like windows disappearing or menus displaying a little strangely but I've had no problems with crashing or lost "work".
Excellent value for money
Give it a try and if you don't like it, delete it and no harm done.