Joel said:
I just stumbled across this is in a search for Captain Cosmic videos (I'm looking for the end credits from the 70s airings of Space Giants, if anyone has this stuff?) - it's only 16 seconds long, but there is a brief discussion of the Holiday Special.
http://www.youtube.com/watch?v=GxuvGphCqnQ
This is one of the few contemporary mentions of the Holiday Special, so it's pretty notable in that regard.
--SKot