If you can't remember someone's name then, ask them "what was your name again?" Out of instinct, they tel you their first name. Then say "Oh I knew that, I meant your last name!" And boom, you get the full name, and you're not rude. Double score.
There's no doubt that a man's mind is behind Facebook. Why? Because it will ask you "What's on your mind?" and then it will put a limit on how long your status can be.