Christopher Beam’s parenthetical comment in Slate is news to me:

When the IRS audited him in 2006 and pointed out the error, Geithner paid the taxes he owed for 2003 and 2004. But he failed to pay the same taxes for 2001 and 2002. In his confirmation hearings, Geithner wouldn’t say why. But the reason is pretty clear: He didn’t have to. There’s typically a three-year statute of limitations on tax audits. If the IRS doesn’t catch you before three years have passed, you’re off the hook. Unfortunately for Geithner, public officials are held to a higher standard. So in November 2008, he went and paid the back taxes even though he didn’t have to. (Fun fact: The IRS can’t accept money it isn’t owed—and after three years, you legally don’t owe the money anymore. In all likelihood, the agency will return the unowed back taxes to Geithner.)