The SIOX demo was *very* interesting.

http://www.siox.org/

It does fast foreground extraction from images based on color.

Last night someone went and grabbed the source and hacked up initial support for this in Blender. We're already behind. :-)

It looks like we might be able to gain some interesting benefits hooking that into tracing - perhaps potrace itself, or perhaps something additional. Oh, and it's also already in as a tool in the developer version of The GIMP.