It's not entirely encompassing, but this piece does a fair job of putting into words the realization which I instinctively and experientially came to after too many years as a faithful Facebook 'early adapter' and a passionate Gram'er. I can't comment on Twitter, because I have never been (and will never be) a user.
Good food for thought, this. (And yes, I'm a teensy bit of a hypocrite, because blogging is social media too, but it has always felt and functioned as more like a two-way conversation and a shared experience than a simple vomiting into the void of 'look at me.' Maybe I'm wrong, but don't tell me if I am.)
My Pinterest policy is decidedly don't ask/don't tell. :)