Just a note to anyone here who may be having this problem: I had an early 2011 MBP, the GPU died three times in three months. Apple charged me $300 to fix it the first time, did it for free the second time because it was still under repair warranty, and then replaced the machine entirely with a brand new 15" MBPr the third time. Obviously, the fact that it failed three times in as many months is unacceptable (and probably uncommon) but if you're struggling with this, do set up a genius bar appointment and see if they can do anything for you.