I was listening to the most recent episode of This American Life and was quite disturbed by the first part of the episode where several high school student discussed the complex set of interactions that occur around the selfies they post around Instagram, which they do regularly. Commenting versus liking. What you say versus what you mean. It's completely counter-intuitive but when you hear them explain it, it makes a lot of sense.
Contrast this to my teenage son, who has wisely figured out that social networks of all kinds are a complete waste of time. He has a Facebook account, but rarely uses it. He had an Instagram account that he stopped using once he lost his smartphone. He keeps up with this friends using traditional SMS and Skype.
I have to think that most people who use social media are somewhere in the middle of these extremes. That said, everyone has their own expectations about what they share, how they expect their "friends" to react to it, and what that reaction truly means. Even I have my expectations, if I'm honest with myself, but my expectations are likely much lower than those teenage girls on This American Life.
The driving force in all cases is attention and desire to be acknowledged in some small way. I just wonder how often we eschew attention in the real world for attention on social media and what impact that is having on our relationships, both short-term and long-term.