Just when I was ready to dismiss YouTube as the place for short, home-made clips of people's cats and teenage pranks, Google buys YouTube and adds a host of features, improved indexing, cleans up the copyright management, and now adds new, functional viewing page features (March 2010).
YouTube has exploded into a living encyclopedia of culture and knowledge. To get an idea of what you can learn on YouTube, check out Kahn Academy's channel, filled with chemistry. statistics, physics, algebra, money & banking, GMAT study, brain teasers and much more. For an awesome list of learning videos from multiple channels, check out the YouTube EDU Partner Playlists page!
Channels like Khan Academy are organized by people. To see the search-engine power of learning using YouTube, try search for a few topics in the YouTube search field. You'll probably need to go through pages and pages of results, and you'll need to learn how to filter out the junk, but it is amazing the depth and span of information and presentation available, for free, 24x7. It is incredible. We have entered a new epoch of society and being human.