I went to a hackathon a few years ago. At the end of the hackathon, my team member (about 10+ years older than me, I am in my early 30s) asked to contact her on Facebook. I told her I didn't have one, because I didn't. Not even an account that I didn't log-in to. She gave me a weird look, then frowned, as if I was shunning her. My other team member looked shocked as well.

I thought it was weird that if you don't have a Facebook account you're kind of looked at weird now.