I built a working 3D printer from the Prusa-Mendel design. One of my friends in Chicago printed the parts on his printer. This was how the 3D printer was supposed to replicate itself and take over the world. Last I checked it didn't quite pan out that way. Worth a try though!
What I learned from this project was that I like building printers. I don't like having to fiddle with them all the time to get them to print. This one was particularly temperamental. It became parts, then trash. So say we all.