Nicholas Shaxson puts a microscope on Romney's finances, the net worth of which is estimated to be as high as $250 million:

Romney’s defense is that he never broke the rules: if there is a problem, it is in the laws, not in his behavior. “I pay all the taxes that are legally required, not a dollar more,” he said. Even so. “When you are running for president, you might want to err on the side of overpaying your taxes, and not chase every tax gimmick that comes down the pike,” says [Lee Sheppard, a contributing editor at the trade publication Tax Notes]. “It kind of looks tacky.”

The specifics of Bain's dealings are even more unnerving:

One cannot properly understand Wall Street’s size and power without appreciating the central role of offshore tax havens. There is absolutely no evidence that Bain has done anything illegal, but private equity is one channel for this secrecy-shrouded foreign money to enter the United States, and a filing for Mitt Romney’s first $37 million Bain Capital Fund, of 1984, provides a rare window into this. One foreign investor, of $2 million, was the newspaper tycoon, tax evader, and fraudster Robert Maxwell, who fell from his yacht, and drowned, off of the Canary Islands in 1991 in strange circumstances, after looting his company’s pension fund. ...

The filings also show a Geneva-based trustee overseeing a trust that invested $2.5 million, a Bahamas corporation that put in $3 million, and three corporations in the tax haven of Panama, historically a favored destination for Latin-American dirty money—“one of the filthiest money-laundering sinks in the world,” as a U.S. Customs official once put it.

Ben Walsh zooms out: