Can the overlay be used as a popup? In Drupal 6 there was the Modal Frame API which made it to Drupal 7 core. However, I'm not sure how leverage the Overlay independent of being an administration screen. Is there any information about this?
Well, actually yes - overlay might be used too if needed. I have just done a quick write-up on this: http://zgadzaj.com/how-to-open-standard-content-pages-in-drupal-7s-administrative-overlay