Comment 4 for bug 1063171

Or we could probably use/add <feature>showdesktop</feature> to unity/plugins/unityshell.xml.in to display a warning like it is already used for various other plug-ins which are not allowed to provide the same feature twice.

The dialogue would look like this:

"Plugin Unity provides feature showdesktop which is also provided by Show Desktop/Fade to Desktop".
 Don't enable Show/Fade Desktop Disable Unity