"found" a new "bug". transparent backgrounds shows as white. sure, maybe transparent isn't supported but maybe we could at least change the color from white to let's say "preview-grey". About bundle it with the app, NO! All qlgenerators should lie under library/quicklook, it's easier for the user to manage the plugins that way.
What we could do is to set up a library/quicklook-link in the gimp-diskimage. That way, people can simply drag the plugin into the folder the same way as they use the applicationsfolder to drag the gimp into it.
It's late over here and I'm to tired to look for faults in the text...