Here is yet another example of Drupal being used as the basis of a custom "distro".
Ubuntu now has UbuntuDrupal which is used for the LoCo's (Local Communities).
Its original aim is to make Drupal easier to setup (which they describe as "painful") and run for these communities. They say that it has grown to be a "general development suite".
Here is where the code is on Launchpad. The numbering of the releases is confusing, since 6.2.0 does not correspond to a released Drupal version.