I'll explain.
In my last birthday I was a little insulted by friends not calling to wish me a happy birthday. It's not that such people are not my friends anymore, it's just that they offloaded some of their knowledge about their friends to some on-line database, so it's a little bit easier on their heads. The same thing happened when we stopped memorizing phone numbers of our dearest, simply because it is stored on a SIM card, and it's easier that way. The problem here was that only people which are members at the same database (e.g facebook) could one keep information about. So people forget birthday dates.
I thought "oh, OK, I don't have a facebook account, so people forget about me". Just this week I considered opening an account, and the strangest thing happened: a friend who's active on facebook had a birthday and told me how insulted he was that most of his friends didn't bother calling him and wish him a happy birthday. It's not that they forget, It's just that they preferred leaving him a short message on facebook: "happy birthday". Being easier than sending an SMS message, leaving a message on facebook seems to be even more insulting.
So instead of enriching this friend's social life, he feels facebook has degraded those. His main dilemma right after seeing all those messages was whether to reply to each and every one, or not. And what to do with those written on the wall?
Is this the case for everybody on social networks? I don't know.
Is there a reason people leave such messages and don't do real social activity (such as calling)? I believe that yes, there is. It is faster, cheaper and doesn't require any human interaction.
I'm still pessimistic thing will get any better before they'll get worse.