As a 3D/2D hobbyist myself who try to use the most free/open source software when I can, blender has become my default 3D software. For the 2D side (texturing and image editing) GIMP was the default one for many years but I start to reconsider it. It may be just me but I think most people start to change their work-flow from a destructive one to a non destructive one. In that regard, GIMP work-flow is mostly destructive. For example, if you apply a color curve tool in GIMP, its effects are "merged" with the layer and you lose the ability to change the curve later on. So I wonder, could Blender be used as an image manipulator in an efficient way or does the compositing in blender lack features for being a great (non-destructive) image manipulation tool ? Then, what free/open source software would you recommend for this task ?
I realize that the question is a bit broader that blender itself but I think it is fair to say that in order to do anything related to 3D, you will need, sooner or later, a good image manipulation software.