Cool. I was looking at Isomage’s hexGIMP and found that the script didn’t work on my Gimp 2.2 on Mac OS 10.4. I groaned in fear of the upgrade hassle waiting for me. But lo and behold, I went to the Gimp download page, found a link to GIMP on OS X by Simone Lehmann. And it just worked!
All I had to do was copy my brushes and scripts from ~/.gimp-2.2 to ~/Library/Application Support/Gimp – and that was it. Awesome!

Thank you, Simone.