Being a design engineer I get to use these 3D printers quite a bit. The downside with the powder based ones is they have a lower resolution than the liquid based. Such as this one http://www.objet.com/3D-Printer/Objet260_Connex/ . These bad boys can pump out .00062" thick layers letting you get some nice detail in your prototypes. The printers aren't cheap either. Average is about $40,000-$100,000.