"I was out running errands today, walking through the city. I remembered, a mile away from home, that a screw had fallen out of my wife’s favorite eyeglasses over the weekend, and that she was waiting for me to fix them. Walking down a city street, I said, “Remind me to fix Amy’s glasses when I get home.” Half an hour later, within a few doors of our house, the reminder went off."

-- http://daringfireball.net/2011/10/iphone_4s