Ron and Andrea had previously released a theme stats plugin - which is great. But, we wanted to take that idea a little further. So, here's a little theme usage plugin of our own:
http://deannaschneider.wordpress.com/
In addition to what's in theirs, this also gives site admins information on whether themes are currently activated sitewide, which themes are not being used, and gives site admins the ability to let blog users that can change the theme see usage information on themes.
Note that the query to pull information is a little intensive on bigger installs, so it only regenerates if the data is more than an hour old or when a theme is switched. It doesn't automatically regenerate when a blog name is changed or when a blog is added or deleted. If you need the absolute latest info - just go switch a theme on any blog and the data will regenerate.
