All this crap works only because YouTube measures only the number of views of a video, and not how many people stop watching it after the first few annoying seconds.
I don't think this has anything to do with the engineering challenges they have to solve at Facebook or the fun working environment. As that code-leak incident hinted some time ago, Facebook probably isn't more than a huge pile of spaghetti php-code. The only motivation of people for switching is greed. Facebook is pre-IPO, so stock options can potentially make some employees millionaires in case of a good IPO.
I don't want to be arrogant, but from the technology point of view Twitter is nothing. Write it in a way that scales better, write it in 170 lines of Scala or 10 lines of Lisp, you still haven't done anything. Come up with the idea before anyone else, get millions of users, that's the difficult part.
The last comment about people's status message is funny. Gave me an idea to write a script, which hides people's status messages, avatars, music they currently listen to, and all similar forms of self-expressing-annoyance, on gmail chat, meebo and all similar.