Fn+F6 misbehaving after Mountain Lion upgrade
If you upgrade to Mac OS X 10.8.4 Mountain Lion and also have Parallels Desktop installed, you will be required to upgrade the latter to version 8.  This new version by default uses the F6 key to "Show and Hide the Parallels Desktop".  To disable this, use the menus "Parallels Desktop" : "Preferences", and click on the "System Shortcuts" tab. to show the above preference, which can then be unchecked or changed to a different shortcut key.