Are you sure about that? Apple lists exactly that as one of the features of Mountain Lion: Go full screen on any display If you have a secondary display conne

Are you sure about that? Apple lists exactly that as one of the features of Mountain Lion: Go full screen on any display If you have a secondary display connected to your Mac, you can take an app full screen on either display. Drag the window to the desired display and click the full-screen button. http://www.apple.com/osx/whats-new/features.html#system http://www.apple.com/osx/whats-new/features.html#system