I am using 13.04 - just upgraded today. I checked in Synaptic and both gnome-control-center-signon and gnome-control-center-unity are installed. In ccsm the Unity Plug-In is enabled. I completely uninstalled both of them with Synaptic, restarted, installed, and restarted again. Still no Appearance icon. I would really like to auto-hide the launcher but no joy unless I can get this back first. I'd even take the one where there are two, as long as I can get to one of them!