Ezra Merkin, the financier who steered $1.8 billion into Bernie Madoff's pockets, officially stepped down today as the chairman of GMAC, the financing arm of General Motors. The move was widely expected given the reputation-shattering events of the past few weeks, a staggeringly swift fall for a resident of New York's richest apartment building and the president of one of the city's most prominent synagogues. But when there's blood in the water, the sharks turn up for dinner, which is why Merkin's art adviser, Ben Heller, says his phone is ringing off the hook.