The reversal ring I ordered finally came in. Basically it allows you to mount a 77mm lens in reverse to an EOS mount camera. This is a full frame shot with the 17-40L reversed. To test out the lens, I brought out some honey and globbed a few drops onto some flowers. Within minutes, TONS of ants swarmed in to feast on the honey.
EXIF info regarding the lens obviously isn't going to work. To fire the shot, the lens was manually stopped down to f16 (yes you can do this with EF lenses), reversed, and shot with the camera in manual mode and two flashes on manual power (about 1/16 power each). The lens definitely isn't an MP-E, but it'll do for now. It's tough to focus at f16, but the working distance and mobility is way better than the 100/50 coupled combo.
Oh, and if ants don't bug you too much (no pun intended), you can see more shots here.