WordPress MU Theme Stats
This is a refresh of a plugin that we released about 2 1/2 years ago. This version is designed for either subdomain or subdirectory installs. Plugin page: WordPress MU Theme Stats.
Adds a Theme Stats option to the site admin menu. The admin panel lists all the themes in use site-wide. At the top of the list will be the most popular theme and a number in brackets of how many are in use. Click on the name, and a drop-down list will appear of all blogs using that theme, with a link to each blog’s home and dashboard.
This plugin goes in the mu-plugins folder.