I mentioned this on WPEngineer, I'd love to see a way to list all widgetable areas that already have widgets installed. WP "knows" which ones are active/inactive, so there must be a simple way to make the UI show there are "X" number of active widgets in ""X" sidebar area/s.

If my theme had 3 widgetable areas (Sidebar, Bottom and Top) and I added 2 widgets to the Sidebar, 3 to the Bottom and 0 to the Top, I'd expect to see something like:

* Sidebar (edit) - 2
* Bottom (edit) - 3

and we don't show the Top at all since it's empty.
Or maybe ...

* Sidebar (edit) - 2
* Bottom (edit) - 3
* Top (add)