It seems that there is a back door to see the number of blogs on a WordPress-MU installation. If you look at the header of any page on a WordPress-MU installation you will see a line like (the XXXX denotes the number of blogs on the system):
The Header section shows stuff that your browser would receive but not display. A fresh WPMU installation headrer will also show the date the system was installed and the link of the main blog.
If you want to test this option you can use Rex Swain’s HTTP Viewer and just type in the blog address and click submit. The popular edublogs.org system returns (today) the following data:
The good people at wordpress.com removed this feature from their system and replaced it with the following message:
hacker:·If you're reading this, you should visit automattic.com/jobs and apply to join the fun, mention this header.
If you want to remove this back door from your installation, open wp-includes/wpmu-functions.php and comment line 77 (on version 1.2.4).
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