From Alex Ragone’s post Not Drupal, WordPress MU (emphasis mine):
So a few weeks ago I blogged about the Drupal installation I was going to create. I had a plan and began to implement it. I had installed Drupal in a Multi-Site configuration but as I worked on the server, I realized that it was too much…At about the same time, I saw Dâ€™Arcy Norman post a tweet about his new WordPress MU installation and how great it was to install and how easy it was to use… I realized that what we needed was an intranet type site and that building it with WordPress MU would be much easier than Drupal. If eventually we needed the functionality of Drupal, our teachers and students would be used to a web based Content Management System and the switch would not be so difficult…With that said, I built our new intranet in WordPress MU.
The most powerful WP Fanboy going!