Using it xdotool, I've done things like used various MIDI controllers to send keystrokes, mouse movements, and mouse clicks to various applications that I use.
You could potentially use this setup to control GIMP, Inscape, Krita, or other drawing applications.
 - http://das.nasophon.de/mididings/
 - http://www.semicomplete.com/projects/xdotool/
Combining with some of the things pmoriarty mentioned, I wonder if you could make this more widely useable.