> Sure, close friends and family will invite you to their social events, but more distant acquaintances will not; you know, the bloke you met at the pub last week and had a 20 minute chat with, or that cute girl you talked to but then she suddenly she was dragged off to a birthday party by her friends. By missing out on the social opportunities you lose the chance to upgrade these people from acquaintances to friends (or even lovers), as well as meet new people.
Man, missing those events is the BEST part about not being on facebook. I have way more than enough stuff to do, I don't need more things with random people. I have enough time for my wife, my kids, and a few outings a month with friends. I can fill that time easily, the thought of having to politely accept invitations from some bloke you met at the pub sounds horrible.