Two excerpts from a short piece on 3D printing by McKinsey. Emphasis mine:

As of 2011, only about 25 percent of the additive-manufacturing market involved the direct manufacture of end products. With a 60 percent annual growth rate, however, that is the industry’s fastest-growing segment. As costs continue to fall and the capabilities of 3-D printers increase, the range of parts that can be economically manufactured using additive techniques will broaden dramatically. Boeing, for example, already uses printers to make some 200 part numbers for ten different types of aircraft, and medical-products companies are using them to create offerings such as hip replacements.

And:

Design is inherently linked to methods of fabrication. Architects can’t design houses without considering construction techniques, and engineers can’t design machines without considering the benefits and limitations of casting, forging, milling, turning, and welding. While there is a wealth of knowledge around design for manufacturing, much less is available on design for printing. Our conversations with executives at manufacturing companies suggest that many are aware of this gap and scrambling to catalog their design know-how.

Incidentally, I'm not sure that the premise of that second quote is necessarily true, regardless of what I believe *should* be the case.