I recently upgraded from 10.04 to 12.04, and there is no show desktop in the launcher. I know I can use Ctrl+Super+D, but is there a way to get it in the launcher?
I just installed the "show desktop" icon on the launcher with MyUnity (see below) and it worked fine. It did not install the icon above Dash launcher, but well below it. That bug has apparently been fixed. This is as of 2012.9.30.