I have the feeling that sooner or later control will be coming:
3D Printable Ammo Clip Skirts New Proposed Gun Laws - Slashdot
When it gets to the point where an individual can just print a gun, licenses and registration for all purchased and prior guns will be required. I also saw an article where a police department is working on a portable scanner like the TSA uses for weapons. Those scanners could be attached to surveillance cameras and if you don't have a license or registration, could be a very substantial fine. Legitimate guns could also be chipped at some point.
I don't think law enforcement would approve of 3D printing your own gun.