We are using CiviCRM profiles to allow members to update addition information. We have marked these profile forms in CiviCRM as 'View/Edit Drupal Account' and 'Drupal User Registration. The buttons appear (and disappear if you remove these settings) in the user profile editing screens. When the buttons are clicked on the user is taken to their Drupal profile, not the screens to capture the CiviCRM data as per this screen shot.
This was working on this site. What changed? We did a general drupal upgrade. Drupal 7.19, CiviCRM 4.2.