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"They're doing something a bit creative, but it's still insulating him from the accountability of the market," said Nell Minow, a longtime corporate governance expert, of Ackman's proposed structure for Pershing Square Holdings. "There are plenty of less intrusive steps that he could take to protect himself from unscrupulous investors."
Minow raised concerns about the notion of a nonprofit organization, however independent, effectively controlling a company like Pershing Square Holdings. "In the past," she said, "it's not been a great thing for nonprofits to have control of for-profit entities. They have different risk tolerance and different accountability."
As part of Monday morning's announcement that it would launch what was expected to be a $5 billion offering on Oct. 13, Pershing Square Holdings disclosed having already lined up early, or "cornerstone," investors who are buying $1.5 billion worth of shares.
Nonetheless, other potential shareholders expressed mixed feelings about the idea of investing alongside Ackman. They noted that despite an impressive performance of more than 30 percent returns so far for 2014—a figure that leaves nearly all the company's competitors behind—the hedge fund manager had also presided over big investment failures like J.C. Penney, which created nearly $500 million in losses for Pershing Square, and expensive gambles like a bearish position on Herbalife, which has gone in and out of profitability for Pershing Square since its inception in the spring of 2012, in the recent past.
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During the course of multiple months, Pershing Square shorted, or bet against, Herbalife at an average price of $48, said someone familiar with the prospectus. So with the stock trading at about $45 as of Monday, the hedge fund's position is in the black.
—By CNBC's Kate Kelly