It beats lugging a tripod around...now that I have a 300mm lens, I need to try this out. I'm going to the Bronx Zoo soon, and not sure if I want to lug a tripod and my backpack around all day long.
Maybe I'm just a shaky kind of guy, but I didn't really notice a big difference after building one of these. I saw that video a while back and gave it a go. It was fun, though!
Maybe you have to give it a little bit more tension, make sure you tighten the string as much as you can, by pulling upward a bit harder. 90% of camera shake is vertical (gravity). Makes sense right? All the string is doing is helping you to add resistance of your own to the equation.
Cool idea, im guessing that it works about as well as the IS on lenses that have it or a monopod for those that dont. Im all about DIY gear though so im going to rig one op and see how it works.