I'm on drush version 6 & can't do a drush status on my drupal8 site, whats the story?
This is a known bug in Drush 6.0.0 that was caused when Drupal 8 changed the way that the Drupal VERSION constant was defined.  This has been fixed in the master branch on GitHub; currently, the only way to use Drush with Drupal 8 is to clone the master branch directly.  There should be a 6.1.0 release out shortly to address this.

For more information, see:

https://github.com/drush-ops/drush/issues/63

UPDATE:  I mis-spoke above.  Drush 6.x supported Drupal 8 until the recent release of Drush 6.0.0.  Now, only the master branch (Drush 7) supports Drupal 8. So, there is no way to get Drush 6 to work with Drupal 8; you must use the master branch.  When 6.1.0 comes out, Drush will correctly tell you that Drush 6.1.0 does not support Drupal 8.