Slate: A grand unified theory of YouTube and MySpace [why so huge] by Paul Boutin
Both YouTube and MySpace fit the textbook definition of Web 2.0, that hypothetical next-generation Internet where people contribute as easily as they consume. Even self-described late adopters like New York's Kurt Andersen recognize that that by letting everyone contribute, these sites have reached a critical mass where "a real network effect has kicked in."
But the focus on the collaborative nature of these sites has been nagging at me. Sites like Friendster and Blogger that promote sharing and friend-making have been around for years with nowhere near the mainstream success. I've got a different theory. The secret to success is to make everything one-button easy, then get out of the way. and give lots of multimedia busy music lights action ~ I guess a lot of people like that... If you think collaborative architecture matters more, click the charts: The same Alexa plots that show MySpace and YouTube obliterating top sites reveal that Flickr, Digg and del.icio.us have plateaued with audiences barely bigger than Slate's. Photos, news, and other people's bookmarks just aren't as interesting as bootleg TV and checking out the hotties. The easier it gets to use, the less geeky the Net becomes, and the more it starts to look like real life.
MySpace's popularity has to do with its puppylike accessibility. (so inaccessible to me! discomfort-causing) A typical page looks like something a Web-enthralled high schooler might have put up in 1996, but with more pics and a soundtrack.
and huh:
-MySpace may let marketers set up profiles for brands. That's a great idea—the same people who'll bitch about Snickers having a page will add Wikipedia as their friend.

rw: Concise comparison of ten YouTube-wannabes Ten video sharing services compared
and: vowe dot net (ceci ne pas un blog) :: YouTube is now bigger than Flickr