I just picked up an Apple 5870 and swapped it into my 4,1. Now menus (either pull downs from the menu bar or ones that appear when you right click) do not highlight the currently selected item. And I just tried to play Portal 2 and it's next to impossible to navigate through the menus without using the keyboard instead of the mouse. I'm going to put the old graphics card back I to see what happens. This is really weird.