When Fortress Investment Group filed to become a publicly traded company earlier this month, it was the Wall Street equivalent of the CIA signing up for Facebook. Being open to the scrutiny of the public is antithetical to pretty much everything that a hedge-fund operator does. But the world of hedge funds isn't what it used to be. Once they were known for being secretive and small--for taking money from millionaires, making winning trades in exotic investments like swaps and warrants and collecting massive fees in near anonymity. The setup was disrupted only by an occasional, spectacular blowup. Over the past four years, though, assets in these funds have more than doubled, to $1.3 trillion, while returns have flagged--and that changes a lot of things...