3D printing is something I’ve written about for quite a while and it has started to become mainstream - HP currently OEMs a printer and an open source solution is available. This article in Technology review titled: Buildings made with a Printer discusses using 3D printing techniques on a larger scale than ever “essentially using concrete, polymers, and other materials in the place of ink”.
The technique described in the article is trying to “extend the capabilities of these machines—making it possible to change the elasticity of a polymer or the porosity of concrete as it's printed, for example—and mounting print heads on flexible robot arms that have greater freedom of movement than current printers.”
It is easy to envision the day when 3D designs are passed around and then built much the way they are within SketchUp today. Our legal system likely has a bit of work ahead of it to be ready for this kind of sharing.
Although these SketchUp 3D models are shared for free, business could sell their Intellectual Property (IP) much the way the music industry is sell songs or the publishing industry or even individuals sell e-books. They wouldn’t have the fixed costs of actually manufacturing the products and can just focus on the variable costs of creating the IP. These techniques also make out-of-print materials available today, increasing their impact.