Bill Ackman is a long term value investor, taking advantage of short term downward moves in prices. He is particularly successful at special situations investments. William Ackman's Pershing Square has a very concentrated portfolio. Bill Ackman's returns have displayed option-like characteristics in 2009 and 2010. His General Growth Properties investment is almost as big as John Paulson's subprime shorts. In May 2009, he recommended GGP stock at the Ira Sohn Conference and the stock returned more than 1000% since then. As a result of that investment, Ackman had a great 2010, returning 29.7%. This is very important because one might be imitating 90% of Ackman's holdings and getting below market returns while Ackman's clients enjoy 30% returns.