3D printers: gimmick or game changer?

Are they the ‘next big thing’ or merely an expensive way to produce lots of ‘small, useless, plastic things’? Apart from adding considerably to planetary waste, what impact will 3D printers have in learning?
http://donaldclarkplanb.blogspot.ca/2012/10/3d-printers-gimmick-or-game-changer.html