Drupal.Org has lots of information (Score 1)

There are potentially thousands of companies using Drupal for intranets (we can't track them due to the free download / no login required). They include small and large companies from BMW to Intel to Pfizer. Much more detail can be found on drupal.org. Here is a link to one post http://drupal.org/node/588636 If you have any other questions, feel free to contact us at Acquia www.acquia.com