I don't think we have a single 3D printer working in linux at the moment.
We should investigate improving CUPS to support 3D printers in a standardised way for starters.
Our first printer to support should probably be fab@home which is a totally open source (open circuit design printer), thats cheap, and we can easily support and afford to test (you basically can probably buy the parts from mostly anywhere to build it, or get their kit. http://fabathome.org/
3D printing will certainly take off in the future, and we should definately get a infrastructure in caser to properly support them (prferably before Apple and Microsoft get one). So that by the time fab@home model 3 is out (which hopefully will be the same cost as a current inkjet, although I doubt it), we are totally ready, and we become the platform of choice for 3D printing