http://yro.slashdot.org/story/13/02/20/0317250/the-patents-that-threaten-3-d-printing (outlines several still-active patents)
http://www.publicknowledge.org/it-will-be-awesome-if-they-dont-screw-it-up (long)
http://www.publicknowledge.org/Copyright-3DPrinting (even longer, but worth reading about patents vs copyrights)
Let the 3d printing patent wars begin!
http://hardware.slashdot.org/story/12/11/21/1333233/form1-3d-printer-and-kickstarter-get-sued-for-patent-infringment
http://hardware.slashdot.org/story/12/10/12/1424250/drm-could-come-to-3d-printers