This has been bugging us at SoSLUG for some time well ok then, me. In compizconfig-settings-manager >> Desktop Cube if you set your number of desktop surfaces to four (4) this gives you your basic cube and quite naturally you would assume given that you can define each of the chosen images for each face, that each desktop image would display the selected image you have chosen. You would think that wouldn't you I know I did. You can add a new image for each surface of the cube each one can be different and there is nothing stopping you from adding to the number of desktops.
Well the good news is that it can but not without a bit more work, and some sacrifice. The work involved requires you issue a complex command on the command line, the sacrifice you need to make is no more Desktop icons on the Desktop. The truth of the matter is that the desktop image that is selected in System >> Preferences >> Appearance >> Background is in fact preserved until the command below is entered into a terminal session.
It is not advisable that you prefix the above command with sudo just use the command as stated above.