Not havnig used facebook, or any friends who use it, I'm not sure what the big draw is.
To people here, I suspect it's about maintaining ties to our less tech-savvy friends and family.
To the general public, like many things, it's about being lazy. Publishing content is difficult. It requires an understanding of the medium (how two right best english) and an understanding of the audience (How do they think? Why do they care?). On top of those two, it requires some actual content. You have to produce material that somebody else will go out of their way to see.
Modern social media takes down those barriers. You can post worthless content, aimed at nobody in particular, and the great data-munching engine in the clouds will take care of the rest. It's like giving soap boxes and loud-hailers to an entire playground of children. Nobody's listening, and nobody cares, but still they shout!
There's also an element of building self-esteem by association - the same mechanism that drives 'reality' television. The slightest interaction with someone of a higher perceived social/intellectual standing (such as 'liking' their post) gives one the illusion of increasing one's own standing, without any of the effort involved in being genuinely popular or erudite.
I think my own objection is to the concept of a personal broadcasting station. My correspondents vary hugely in communication style, interests and technical ability. Sometimes IRC is the right tool for the job, sometimes a paper letter is more appropriate. Either way, what I say, and how I say it, is entirely dependent on who I'm saying it to. I never want to send the same message to everyone, so why should I use the same system for everything?
