Interesting paper attempting to show that even current open source 3D printers can pay for themselves:
http://www.sciencedirect.com/science/article/pii/S0957415813001153
Now, as the comments in the slashdot thread quickly find out, the methodology is probably pretty flawed (a few very expensive items skew the conclusion):
http://tech.slashdot.org/story/13/08/01/0019259/study-finds-3d-printers-...
Still, it is not hard to guess that 3D printers will take over some niches fairly rapidly. I was impressed today when playing with my brother's kids to find a set of weird wings for their lego minifigs: dad had just printed them, and at least for this kind of piece the tolerances of his first generation makerbot are OK. (Lego pieces are surprisingly exact objects)
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