3D Systems has been buying up companies in the field for a while now (bitsfrombytes, botmill, Z corp and so on, more here: http://static.cdn-seekingalpha.com/uploads/2012/11/19/6383-1...)

They are bound to have a pretty big portfolio of 3D printing related patents. A case of 'join or be sued'? Strictly speaking, wouldn't even be against the law, would it?