YouTube has already been one of the my favorite sites for quite a while as it is just loaded with a wide variety of really creative and funny home-made videos. Personally, I enjoy finding home made videos, old commercials and some music performances on YouTube. I've also used it as a video resource when people want to view certain speeches by famous people. I do think one of the small problems I've run into YouTube as a librarian is numerous times I've had students who want to be able to save videos from YouTube and other sites right on their flash drives or PowerPoints either for assignments or personal pleasure, however for many reasons copying and saving videos is not usually an option other than copying the embedded script or copy the URL. Sometimes I think some students especially younger students who were used to Napster and similar places are still wishing for the age of free content with little regard for copyright.
All that being said YouTube and similar sites are some of the better 2.0 type sites IMO. I've always been a film and video lover and places like YouTube allow everyone to at least be able to view and share all kinds of old and new videos and it allows for pretty easy keyword searching as well. In the age information sharing, YouTube is a valuable resource and tool. On this post I've included (the embeddable player of) one of my favorite videos on YouTube about librarians... it is a mock video called "March of the Librarians" posted by the user "nnnicck" on YouTube parodying librarians and the documentary March of the Penguins. I think its pretty funny.