Susan Etlinger, an analyst at the Altimeter Group, said society was adopting new behaviors and expectations in response to the near-ubiquity of Facebook and other social networks.
“People may start to ask the question that, if you aren’t on social channels, why not? Are you hiding something?” she said. “The norms are shifting.”
I don't know if people ever think that because you're not on Facebook, you are hiding something. It can be frustrating to organize an event and try to remember all of your friends who aren't on Facebook, but besides that, I think a lot of my friends have a bit of respect for those who can get away.
As soon as something better comes along, or as soon as Facebook screws up big (like GoDaddy big), people will move to greener pastures.