I checked the Use the F11 key for standard shortcuts in the preferences>keyboard. So F11 shows the desktop...sometimes! If I have a screenshot or note or email open, F11 behaves. But if I have Numbers or Calendar open, when I press F11 the screen flickers once, the starts opening Message, email and does not clear the open screens to show the desktop. Am I missing something or is this just another Mavericks issue that Apple ignores thinking it [and the users] will go away?