I am facing a very peculiar problem, the 'Appearance' icon in 'System settings' has disappeared and now I cannot change the background or control the unity. Any ideas how to get it back?
This seems to be something Gnome has changed, since I am not using Unity (sticking to Gnome-Shell) and the same happens to me.
You will find another Icon under the System Settings (I am not sure how stuff is called because the default of my system is not in English) called Background. You can also access it clicking on the desktop with the right mouse button and choosing "Change Background".