Plugin and theme User List

On a multisite wordpress installation, I would sometimes like to know for a certain plugin
– whether it is active in any site at all
– if it is active, how many sites use it
– exactly which sites use it

The same thing goes for the themes.

This would help greatly in adminstering plugins and themes. It allows to address only those site administrators, that actually use a plugin, if something has changed. It would also help to find out whether a plugin is superfluous and can be deleted.