Development versions of GIMP have had symmetry painting mode for a little while now. I finally got around to compiling one of these development versions on my Cintiq. I don't know how generally practical it is as a feature to producing art, but it sure does make it easy to knock out some interesting designs.
The characters in my shmup side project are mostly symmetrical, I might find some use for it in that too.
This is a doodle from today's weekly status meeting at Neoglyphic Entertainment. Sketch and lineart were done in the one meeting with an unstable development version of GIMP.