Billionaire Bill Ackman has never been reluctant to blaze trails. He became the first hedge fund manager to get directly involved in a hostile takeover when backed Valeant Pharmaceuticals' $50 billion bid for Allergan. And Ackman is leading a costly and very public crusade against Herbalife, which he says is little more than a pyramid scheme. Now he's considering listing his offshore fund in London, a move that would free him from the whims of wimpy investors. But potential shareholders should beware. Ackman's recent record is mixed, at best. And his brand of activist investing will never be as big across the pond as it is in the U.S.