Ya know, this is something I want to do someday. I went to a local conference and went to a Kinect seminar where the host (he works for Microsoft) was talking about leveraging the new API for Kinect, and that by using it, you can somewhat get a 3D model of an object in space. The example was pretty darn accurate too, he modeled his mouse, and each point corresponded (from the point of view of the kinect) pretty acuurately where it should be.

Very interesting, but for simpler parts, I'd just measure with some calipers and such. 3D printing is awesome, I have seen/used them at college (I was in ME) and it seems "cheap enough" to build -- $900-1300+ depending on size of the object you want to print is.