Not necessarily in it's infancy, there was a company in Grand Haven doing 3d prototyping with one at least 15 years ago when I was there. I could see some nice cab designs coming from this too, and yes I think there was a company doing a house and a guy doing and entire building using one. Did you see the article on cnn in the last 2 days? They're working on an ink pen one that can do the same thing. It's a whole new world out there.

A 3-D pen that lets you draw objects in the air – What's Next - CNN.com Blogs