It's miraculous to see: Press a button, make anything you want. But will it transform the economy?
Probably not. Except...
Unlike earlier big-deal technologies (like, say, the tractor) 3-D printing won't really replace what came before... Still, 3-D printing is amazingly powerful for personalized applications. Right now, there are 30,000 people walking around with 3-D printed titanium hips, which are less expensive than conventionally manufactured artificial hips.
There are a lot of niches for 3D printing, even if you restrict yourself to only working with plastics/sintered metals. Replacement parts for equipment ginned up on demand, for example. Anything that requires some sort of customization (prototypes, limited run fabrications, medical prosthesis, etc.) can potentially become cheaper to produce with these sorts of tools.
Oh, and houses. Don't forget about houses.
So... yeah. 3D printing may not transform the economy, but it is going to have a heck of an impact.