Julian Robertsons golden years of semiretirement are turning out to be golden, all right. The 75-year-old Tiger Investments chief scored his best investment return ever in 2007, raking in a stunning 77.7%, according to Fortune. Not bad for a guy who officially closed shop in 2000. But dont assume he is bullish on the U.S. market. Robertson roared in 2007 and early 2008 by pouncing on U.S. subprime woes, using derivatives called curve steepeners to exploit arbitrage swings between two-year and 10-year Treasuries.