For linux users.

Molly raised the subject of this little utility, 'ChangeImage'. http://registry.gimp.org/node/25571 It is a standalone windows application and not a Gimp script/plugin but it does make nice Gimp .ggr gradients.

A very quick demo of calling this from Gimp using RobA's Shellout script.

http://youtu.be/AfWVoYBmIok

caveats:
This is 32 bit linux - PClinuxOS
I never managed to get Shellout greater than ver 0.5 to work in linux
Using WINE ver 1.4 , I found the latest ver 1.6 breaks several of my win utilities so I reverted back.

note on youtube
If you can not hear any audio and/or the video is very small, not my fault, it is youtube flash settings
adjust the youtube player

That is great Rich. Glad you got to use it, I don't think anything beats that utility, I also like the way you can see as you go the way the gradient is going to work.
When I was using windoze, I was making pictures with frames and I would use that utility to make my frames from a gradient taken from the picture.
I have 64 bit so I don't know if it will work for me, but I recommend it to all Windows users. I haven't even installed wine yet on Fedora19. I haven't found any need for it yet.
Thank you for your research.