Pinta is a nice bitmap editing tool, simple and yet powerful, for Linux/MacOSX/Windows
Jonathan Pobst it's creator and maintainer is focusing his energy on some other ventures and left it untouched for some time know.
Cameron White forked and started to make it tick again, and now Robert Nordan and other people in the project discussion list http://groups.google.com/group/pinta?hl=en, including me , are starting to organize a full project team around it, at github (my fork https://github.com/monoman/Pinta).
I approach this with a more systemic view to have something like the MonoMagic App Wall (chose another name because a store would emphasize a commercial offering), with apps that may be easily installable/usable on any of the miriad platforms where Mono/.NET is available, Pinta could just be the forerunner.
Imagine an iPad/Android version of Pinta, with your drawings/photos synced to your personal cloud storage, so that you can take your editing session back at your Linux notebook later...