Automatic home-building?
Concrete isn't a very eco-friendly material, but the blog posting of Next Big Future: Built for Speed: Printing Buildings is really interesting on the "how to build more homes for people, better and faster" topic. What I don't get yet (and, yes, that's because I haven't read about it in detail) is how you can build on top of concrete when you have the issue of curing it -- unless you build really slowly. But I'm sure I'm just missing something...