I'm kind of a casual gimp user in that I can do simple things with it and when I need to know a little more, I dig deeper into the docs. Maybe others in your intended audience are similar. I'd like to learn more about things I see on the menus but don't use because I don't know why I need them, like layer groups, layer masks, and alpha channels. The other major hole in my gimp knowledge is about the scripting features.
