yeah, that would be the worry. Of course, if social networks produce real value, then those who choose to opt-out would be at a disadvantage.

Who's to say that people won't opt-in but be very selective of what they inject into the system?

I find it... unlikely that the average teen will be selective about what they inject into the system. The average teen goes out of his way, sometimes way out of his way to shock parents and society.

Sure, there are a few teens who will try to appear normal and responsible, but I don't think that will matter. the average decides what is acceptable.