I'm pretty familiar with YouTube. I've been in many situations (as I'm sure everyone has) when I'm forced to watch videos other people find funny, and when I force others to watch videos I find funny. (Everyone watch the Drunk History series. They're only like 7 or 8 minutes long and awesome.) Some of the time I find YouTube to be a little annoying because not everything people video is worth watching, but most of the time I find it to be an amazing concept. Just as blogs allow individuals to become authors, YouTube allows them to become directors.
I think that YouTube can be very beneficial for libraries. I know from experience that most students in an academic setting have no clue how to find books, let alone electronic journal articles in their school's library. I also know that most will not ask a librarian how to do so. I would think that creating how-to YouTube videos illustrating how to find materials in the library would help those students tremendously.
Looking for library videos on YouTube immediately brought me to an episode of Mr. Bean that features the man himself going to extreme lengths to avoid the legendary library taboo of making noise.