In the U.S. version of TV show The Office, boss Michael Scott confesses: "When I discovered YouTube, I didn't work for five days. I did nothing. I viewed Cookie Monster sings Chocolate Rain about 1,000 times". Now, of course I don't think this is something that any of us should take on board, but I think it does a good job of summing up YouTube's time-wasting powers! I've never really thought of it as being useful for anything apart from this.
Here, Michael Scott shares his thoughts on Wikipedia.
Some of the library videos out there are pretty informative but I can't really see that the effort would be worth it in most cases. What we maybe could use video for would be mini-tutorials as part of Computer Assistance. Having said that, I'm not sure that people with not much computer experience would be interested in learning this way.
For something book-related, check out Bookmans Does Book Dominoes.