I'm pleasantly surprised this is being discussed at the top of HN.
I feel like 2 years ago people would pile on about how unusual it was to not be part of social media, how there is little argument against leaving, or how you must be seeking attention or must be anti-social. Well, as a very social 20-something, I left Facebook 3 years ago, myself a heavy user with thousand+ friends scattered around the world, and it has made zero negative impact on any aspect of my life ('invitations to events' or 'keeping contact' is the typical fear against leaving, and it continues just as seamlessly [1] - people don't stop caring, thinking, or reaching out to you just because you leave Facebook, and vis versa), and it has easily been one of the top 5 or 3 decisions I've made in these 3 years. It's the equivalent of cutting out unnecessary yet significant things, or simplifying your life so you can remain mindful of the bigger goals. This may sound like something cheesy from the 4HWW, but I nonetheless think that kind of mindset is right on.
Now I see more people leaving Facebook who I wouldn't have imagined doing so a few years ago. Perceptions will remain divisive for some time, but I can see "avoiding social media" as gaining some real cachet as "I don't fuck around". Regardless of whether there is actually a correlation with avoiding social media and being a more serious, goal-oriented person, I do think mainstream perception will continue to change for the better away from the stigmatizing "Wow is not on , what's his deal?"
[1] Lightweight messaging apps, especially for international contacts... certainly not the whole investment of 'social media' since it's nothing but the messaging.