Tyson Balcomb quit Facebook after a chance encounter on an elevator. He found himself standing next to a woman he had never met — yet through Facebook he knew what her older brother looked like, that she was from a tiny island off the coast of Washington and that she had recently visited the Space Needle in Seattle.

“I knew all these things about her, but I’d never even talked to her,” said Mr. Balcomb, a pre-med student in Oregon who had some real-life friends in common with the woman. “At that point I thought, maybe this is a little unhealthy.” [See & Read More]