People often describe the FDM (fused deposition modeling) process used by most desktop 3D printers as 'like a hot glue gun extruding plastic'. Well, check out this video of a DIY hot glue gun 3D printer.
Who wants glue to be the next 3D printed material on Shapeways?
Saw this and was interested, we've been doing something similar only on a larger scale here at Taubman in Michigan. Check out one of the videos I made on the project. http://www.youtube.com/watch?v=sKJ5iE2o4LM&feature=g-upl