Well I guess a hijack of the thread into "3D Printing" is better than into economic theory.
This RepRap approach is a very interesting development, even though limited to thermal
plastic extrusion at its start. It is certainly an interesting subset of Computer Aided
Manufacturing (CAM).
There are of course other manufacturing technologies that can be similarly adapted.
Even the simple single stage 3D Printing idea is apparently exploring other materials in
addition to thermal plastic. (I would think the wide range of "Epoxy Putty" and similar
mixable compounds could be made to function well in this setting and offer the digital
exchange of mixing formula, for varying the resulting properties.)
The 3D carving of molds is an obvious companion engineering classroom technology,
and in the case of making molds for aluminum casting, should appeal to the same
"Social Conscience" that motivates these projects. (I've done some green sand casting at home and recycling aluminum cans is a no brainer. Also, you can download all the
information needed to construct a metal melting furnace.)
I would think a multistage process would be in order, where your rough "printed" parts
are finished using CNC, like this:
http://buildyourcnc.com/default.aspx
(Notice that they have a forum and an interest in "3D Printing" as well.)
Luck;
Ken