Evan Williams (left) and “Biz” Stone, founders of Twitter, use the social-networking service at the company's headquarters in San Francisco on April 13, 2009.
Image: Peter DaSilva — The New York Times/Redux
Evan Williams (left) and “Biz” Stone, founders of Twitter, use the social-networking service at the company's headquarters in San Francisco on April 13, 2009.
Image: Peter DaSilva — The New York Times/Redux
