How to hide all desktop icons in 12.04 and later?
It's in gsettings (& dconf-editor), to do from cli use
gsettings set org.gnome.desktop.background show-desktop-icons false
From gui open dconf-editor (install dconf-tools) as in screen
The MyUnity application (in the software center) has a lot of useful features for customizing Unity, including the ability to hide desktop icons. The newest version supports 12.04.