Drupal 6.8 and Drupal 5.14 are slight updates to Drupal 6.7 and 5.13, removing an incompatibility with versions of PHP before and including 5.1.x released in the earlier versions. The 6.7 and 5.13 releases fixed problems reported using the bug tracking system, as well as critical security vulnerabilities.
Upgrading your existing Drupal 5 and 6 sites is strongly recommended. There are no new features in these releases. 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.