@Josh, Doggo: I don't actually think it's geared at all - it looks like the roller under the back of the belt is in direct contact with the rear wheel.

The best part about this video is the narrator giggling as she says, "you can take it down stairs..."

These folks are built a couch bike:
http://www.bikeforest.com/couch_rental.php

I was first introduced to this on the patio at Juan in a Million (best breakfast tacos evah) in Austin, where we never saw a fly. I was told that bugs' compound eyes can't deal with the refraction (light bending) in the bags, so they steer clear.

This doesn't sound too far-fetched to me, considering that it's thought that flying insects use the horizon as a reference to stabilize their flight. The bags of water, and the resulting visual effects, may have the effect of creating a no-fly (heh) zone in the vicinity, where the insects' flight instrumentation goes haywire.