Yes, that's the network effect. It's useful because it's used. It's a fact becuase it's a fact because it's a fact, etc. And it's not just young people either. Most of the people who force me to reluctantly use Facebook sometimes are actually older than me.

But I want to know if there is anything genuinely useful about the form of communication that is Facebook. I think there has to be something, or it wouldn't have become what it is.

Maybe it's that the default mode of communication is spam. Maybe it's that what is said on Facebook carries less weight and hence requires less effort to say. Maybe it's that statements need no reply there. Maybe it's like the village square where people hang out so they don't feel lonely even if they don't have anything to say.

I don't know what it really is. But us hackers should ask the question because it might tell us what to create in the future.