I spent some time on the wpmu forums, and was inspired to create this little script that generates some statistics.

The source is here. N.B. that the first line includes a ‘proprietary’ set of libraries which I’m not distributing, but all it does is handles the MySQL connection and creates a query() function for (my) ease of use. Also note that all of this information is either extracted from the database (aside from a little arithmetic here and there), so you’d do well to make sure MySQL query caching is turned on if you expect to use this type of thing with any regularity.