Uses for 3D printers

I commented here on the arrival of 3-D printers, so was interested in this item suggesting that they could be used to "print" your own gun at home!
At the moment, I imagine it would be possible, it least in theory, to "print" a replica gun (although it might be just as easy to carve one out of wood!).  However, right now it's difficult to visualise that the current generation of printers - which make things out of plastic - could produce a workable gun.   But who knows what such printers could be capable of, as technology advances.