Roamy here. I saw this Popular Science article on printing out an entire airplane wing. (Watch the video “Why I love my 3D printer” – it’s cute.) Rapid prototyping is a misnomer now, because it’s not just for prototypes any more. It started out as wax or plastic parts that could be warped or distorted from the original design if you didn’t pay attention to what you were doing, but still a useful tool for design and manufacturing. Now you get aluminum or titanium parts that are ready to use, with less machining waste and usually less time.
NASA is looking at rapid prototyping as an essential part of a manned Mars mission, because you can’t possibly take spares of every single part you might need, and you can’t bring an entire machine shop, either.