I was the lead developer and team leader for Sony Music's Drupal-powered artist website platform. The platform was a highly-evolved Drupal 6 environment with custom modules, install profile and base themes to support the needs of the artists and labels. When I left in 2010, there were nearly 200 sites running on the platform, with around 3 sites being launched every week.
One of the major accomplishments of the platform is the vast use and customization of Drupal's internationalization features to provide localized environments for many of the sites. Some of the sites have over 20 localized environments in over a dozen different languages. A lot of the work done for this platform made its way into Drupal 7.