How camera lenses are made
Considering YouTube is less than 1.5 years old, it already contains an amazing amount of interesting stuff. See for instance this short docu-thingy: How camera lenses are made.
I can see a future where a lot of the less essential information we need and want is available on the web, not just as text but also in video form. Text will not be replaced, but I have to admit that watching something in video form is more entertaining and holds my interest better.
I concede though that if you need to learn something for deep and serious application in your life, probably text is better.