Upgrading your existing Drupal 5 and 6 sites is strongly recommended. There are no new features in these releases, but we fixed some notable performance issues too. For more information about the Drupal 6.x release series, consult the Drupal 6.0 release announcement, more information on the 5.x releases can be found in Drupal 5.0 release announcement. If you use Drupal it's strongly recommenced that you update it to the latest version.