I just updated my rMBP which I've had since last August (hadn't done it for a few weeks, so the software updates may have been old). It's probably also worth mentioning that I have a bad habit of just putting my Mac to sleep, so this was the first hard reboot for a few weeks despite having put it through quite a bit of strain while rendering and editing photos. When I restarted, I noticed a sort of spasm when I scroll, both vertically when browsing safari, and horizontally, for example when swiping between my dashboard and desktop. Even my icons stutter slightly when I hover over them. The effect is hard to describe -- it's definitely not the scroll lag which people with rMBPs sometimes complain about; it's more of a subtle flickering/spasm, almost as if the screen is catching on something as I scroll. The problem only seems to occur when I have programs like Photoshop/Sketchup/AutoCAD open, so I'd assume it has something to do with the GPU. I reset my PRAM (I'm still fairly new to Macs and am not sure this was even relevant to the problem, but it's the one of the only troubleshooting options I knew how to do haha). Any suggestions?