Same story for 2011 Q1 MBP, it seems like the Graphics are defect for several models and suddenly started to fail for several customers about now... +800 posts, NO RESPONSE FROM APPLE!!
I had this issue pop up in late 2012/early 2013 on my 2011 MBP. It was just visual at first but after a few months, it turned into system crippling hangs.
I replaced my mobo this past summer under Applecare ($500 if you don't have coverage). Guess what they replaced it with? A logic board that exhibited the same issues two months later.
A friend of mine just started experiencing the glitches on his 2011 MBP.
My current workaround is to make sure that I unplug all external monitors, and shut down with the setting that no app windows get reopen. If you have an application that forces the discrete GPU to be used (Coda, for example), it can cause startup hangs.
https://discussions.apple.com/thread/4766577