This was already pretty much finalized in http://drupal.org/node/496728 but I thought I should cross-post it here.
* The Drupal.org webmasters team does not expire or change usernames for any reason. This data is considered integral to our community's history.
* If there are legal concerns such as trademark infringement, the user should contact the Drupal Association http://association.drupal.org/contact. All requests must include required documentation to prove identity and trademark holdings. The Drupal Association may or may not act on requests, depending on advice from legal counsel.I suppose we could mention something explicit about "If you want someone else's username, send them a mail through their contact form and see if you can convince them to change it," but people will probably figure that out without our explicit mention. Morbus has concerns about the fact that authenticated users can change their own usernames, but this has been a feature of Drupal.org since time immemorial so if we want to change that we should discuss it elsewhere.