Between Tuesday’s east-coast earthquake and the approach of Hurricane Irene, we are seeing how social networking can become a valuable security-communication tool in a crisis. The Twitter storm told me everything there was to know well before the news stories started to appear, says Bill Brenner. In a crisis, communication is key, and social networking allows it at a speed we’ve never had before. Thanks to social networking, we have safety in numbers, he says, or something close to it.”]