Michael just sent this to me. It's too good not to re-post:
Hacking the versatile Frosta stool from designers Andreas Bhend and Samuel Bernier is quite possibly the ultimate IKEA hack: the Draisienne bicycle. The duo's ingenuity used a standard Frosta kit and custom 3D-printed parts from le FabShop, a Paris start-up where Samuel works. Check out their project in the video: If you'd like to try your hand at building this bicycle, they've uploaded everything you need to know: a PDF with full instructions and the 3D printing files at Makerbot Thingiverse. If you don't have access to a 3D printer, you can order the parts directly from le FabShop.
(Images: Andreas Bhend and Samuel Bernier via Instructables)