I've taken Scott Lembcke's Chipmunk Demos (which are included with the Chipmunk source), and translated them into Ruby, using Gosu for display (sort of). In their current state, they are uncommented source that doesn't actually do the drawing with Gosu directly, but instead uses only OpenGL (as do the original demos in C). As such, they're pretty good as Chipmunk demos (except for that 'no comments' thing), and do a passable job showing how to do with raw OpenGL what would be better done using Gosu::Image, but they're not exactly Gosu demos in the normal sense. At some point, thoguh, I'll be creating a branch which *does* use Gosu::Image for drawing.
Getting this code to run at all is fairly complex; the most problematic requirement is that you can't just download regular 'release' Chipmunk and use that. Instead, you must use Chipmunk's SVN Trunk, at least until Chipmunk 0.5 is released. You can see the README.txt file for more details (though, not *many* more details).
This is all pretty unpolished at the moment, but I figured it might be useful to someone. Have fun, or at least don't gouge your eyes out after looking at the code!
http://bitbucket.org/philomory/chipmunk-demos-ruby/
