I'm running a scaled resolution (the one that is 1 notch smaller than default in the preferences - think 1680x1050?) and was having pretty bad lag or "jittery-ness" when using Mission Control under mountain lion. I found a tip when browsing the Apple Discussion forums that drastically improved/removed any lag that I had and made all ML gui animations perfectly smooth. Apparantly there's a quirk with the Intel driver that needs fixing meaning its not transitioning between the two graphic chips very smoothly, so if you go into your Energy Saver settings (in system prefs) and uncheck the 'Use automatic graphic switching, then it always uses the high-end chip rather than constantly switching between the two. Obviously not ideal and would only recommend if plugged into the mains as sure it drains the battery - but as a temporary fix my rMBP is now running smooth as can be! Hope this helps. Richard.