Warren Buffett may be the greatest investor ever. But his long-term philosophy, which was ridiculed as he avoided the dotcom boom--and vindicated as he avoided the bust--is being scrutinized once more. The buy-and-hold billionaire is up to his ears in exotic investments known as derivatives, which are used to bet on things like the weather and the direction of interest rates. Derivatives were at the core of the 1994 bankruptcy of California's Orange County and the 1998 demise of hedge fund Long-Term Capital Management. Buffett once called derivatives "financial weapons of mass destruction," so you'd think he would steer clear.