Aaaaaahhhhh......YouTube. What a great innovation. I have wasted many an hour clicking on a specific video and then clicking on any video even remotely related at that video. YouTube has that Amazon thing going - "If you like this, you'll probably like this." YouTube doesn't exactly word it like that, but you know what I mean. More often than not, they are absolutely right - I do like the related videos that they suggest. That's how I get lost on YouTube.
Even though YouTube can be extremely useless (but fun), it can also be used as a learning tool, as long as the user is pushed in the right direction. There is a virtually endless number of instructional and/or educational videos on basically any topic or subject. Navigating around YouTube is really easy - I like the basic search feature of the site.
As far as specific videos go, I usually try to find music videos that I can't normally see on music video channels, or I look for soccer related chanting and singing. Aside from the Philadelphia Union, which begins playing May 2010, my favorite soccer team is Liverpool FC. The fans are (usually) pretty boisterous, and I enjoy watching videos of them singing on the famous Spion Kop. Although there are a lot of songs and chants to choose from, my favorite is a pretty simple one that isn't sung as often as it once was, but is still classic. It's title is "We Won It Five Times." If you type that phrase into the search engine, there are many clips of it.