I'm running a Mid 2011 Mac Mini with these specs:
2.7 GHz i7
8 GB 1333 RAM
AMD Radeon HD 6630M 256MB
10.8.2
My main issue is when I'm playing a game, my second monitor start flashing uncontrollably. I play fullscreen on my main monitor and have my Dock on my second monitor, and during the game it's constantly flashing during the game. Also, if I move anything on the second screen while the game is in progress (this includes the loading screen) that flashes as well. What I mean is if I had a website open on my second monitor and I scrolled up/down on it while in the game, the screen would flash between the pre- and post-scroll.
Second, I was wondering if there's any way to keep the mouse within the game window during a game? When I have the screen unlocked I'm able to move my mouse to the edges to move my view just fine, but when it comes to doing lots of clicking, like kiting or in a teamfight, my mouse often goes outside of the game window and then clicks on something on my second screen and then the flashing begins.