I recently played Left 4 Dead 2 on a MacBook Pro from late 2011 with OSX Lion. At fIrst all went well and then I tried to play via the PS3 Controller and loaded some cfg files from the web. Suddenly, I do not know when exactly, I could not look arond any more. Neither by using my mouse nor the trackpad nor the controller (actually this never worked). I started some troubleshooting by loading some other cfg files (including the default one), by setting m_rawinput to 0 (was not activated anyway) and by deleting the whole cfg folder and redownloading it via Steam. I even copied the game files from a friend's MacBook to my Left 4 Dead 2 folder - still no mouse movement. Steam Cloud is turned off. My mouse DOES behave normally in the menus and in the game itself I can shoot, change weapons etc. but I cannot look around. I will give it a last try by redownloading everything and reinstalling Steam but I don't think this will work.