I recently updated my MacBook Pro to OSX Mountain Lion. I had played through Episode 1 on Lion with no issue. After updating earlier this week, I decided to start playing Episode 2. I immediately noticed extreme mouse lag when I got into the game. I am using the trackpad on my laptop. The strange part is, I don't have the mouse lag in any other program, nor do I even have it in the menus - only in the actual game itself!
I'm not even sure if I can call this mouse lag or not. It's just very jittery. Sometimes it's smooth for a second and other times it acts as if it isn't receiving any input at all. I tested this with a USB mouse as well that I have never had issues with, and the same thing happens.
I went back and started a second playthrough of Episode 1 and now I am experiencing the same issue there as well. It must be something with Mountain Lion but I'm not going to change that. Has anyone else run into this issue and maybe even fixed it?