I've heard of this kind of usage before, and it caught me totally by surprise. Google must be loving this. It's no longer a funny/music/weird video portal, it's now a place where people go to find information and knowledge (even more since they moved googletalks into youtube).
Amazingly, YouTube is the number two search site after Google - http://www.tgdaily.com/content/view/39777/113/
7.6 billion for Google and 2.6 billion for YouTube as of last August.