I have a "friend" from university that I occasionally emailed links or articles. Months went by and he never wrote me back, so I questioned him about it and he said "you know I've been busy with the wedding and all".
"What wedding?"
"Yeah I got married, I guess you don't go on facebook. I don't reply to emails, just facebook me next time."
Obviously our friendship fizzled away, and wasn't worth keeping up, but some people only use facebook and won't communicate with people other ways. It's weird.