Every time I hear more about this domain (typically from folks like iamwil at CubeHero) I become more excited by the possibilities. It's a enabling technology, so looking for a "killer application" is probably the wrong way to think about it: the impact is likely to be more fundamental and spread across a variety of small use cases for a long time until it's ingrained in our culture. I still remember walking into a VC's offices and seeing a row of neatly-printed 3D 4-polytopes sitting along the counter to welcome entrants.
Sadly, it's the one piece of equipment where I can't think of even a tangential application in crowd labor, so there's not one here at the office yet. I expect this'll be as ubiquitous as a 2D printer in offices within a few years, though.