Large square "pixels" on Macbook pro screen?

I am using a 15 inch 2011 MacBook Pro runningMac OS 10.7.5 and am having some graphics issues on my screen. I have gone to the "genius" bar twice already for this issue and they have taken my laptop to run tests but were not able to recreate the issue and are not willing to do anything about my issue even though I have documented these problems by means of screenshots (but that's a whole other discussion).

After a week of getting my laptop back, I started getting issues again. See images below. They tend to crop up after about a week of not shutting down or restarting and this has been recurring for about 6 months now. I was wondering if anyone has seen this before (the "genius" people seemed pretty stumped when they saw this).

Thanks!