San Francisco's Center for Sex and Culture played host on Saturday to the city's annual "Masturbate-a-thon," an event its organisers said could draw up to 120 people from across the United States aiming to have a good time with themselves. Carol Queen, director of the center, acknowledged that the event is unusual -- even by San Francisco's standards. The permissive city, which helped ignite a debate on gay marriage last year, tolerates many sorts of sexual behavior but masturbation seems a topic that is off-limits, she said. "Even people who are sexually frisky might have the bias that many Americans...