I'm an inventor and I have at least 9 patents to my name, so I was interesting in what patents are out there for 3D printing. It looks like Stratasys has been working in this area for a while, but I noticed that their original patent is now no longer under patent protection:
5121329 Apparatus and method for creating three-dimensional objects was filed in Oct 30, 1989 and issued Jun 9, 1992.
For patents issued before June 8, 1995, the patent term is either 17 years from the issue date or 20 years from the filing date. That means this one ran out in 2009. And it's a doozie too because it basically covers CNC based plastic deposition printing!