Jay Leno uses this technology to produce hard to find plastic parts for his antique cars. Really, you can create anything with it that can be created with plastic - prototypes, combs, trim, even limited use guns. At least all the ones that I've seen use some type of plastic or plastic-composite material in the printing process. The printing process lays down very thin layers of the plastic material, from the bottom layer to the top. Youtube videos show the process very well.
Many of the items that are printed are first scanned in using a 3d scanner then sent to the 3d printer to be built. I'm sure that many of the 3d modeling software packages are being built to send completed models to the 3d printer for printing. To get into this, an engineering degree would help with a focus on 3d modeling. If you have these skills, you won't be limited just to 3d printing, but you will have a whole host of lucrative opportunities available to you. The first few years would be the most difficult because many jobs want you to have a certain amount of experience before they hire you into something like this.
I have no direct experience with this, but have read a few articles on the subject.