Even the best sites need to be upgraded over time. Mediacurrent initially built the Emory Michael C. Carlos Museum in Drupal 5. Over time, they have done maintenance releases and feature enhancements for Carlos, but software, as well as websites, have a limited lifetime.
As 2012 rolled around we noticed that most of the Drupal 5 modules had reached their end of life and certainly no new modules were being created. The lack of updated and new modules severely limited what new feature sets Emory could incorporate into their site - so it was time for an upgrade!