I know it's basic knowledge, but I really can't find any option to change my default file association for graphic files in Thunar, always Gimp is running. I've installed a gThumb but still Gimp starts. I'll be grateful for a hint.
I'm using Thunar 0.8.0, and this is what works for me. In the file manager, right-click on the file you want to open. From the pop-up menu, select "Open With Other Application". A dialog box will come up with a list of applications; select the app you want to use, and hit the "Open" button. Make sure you have the "Use as default for this kind of file" checkbox checked. Unless I'm misunderstanding your problem, that should do it.