The Government Accountability Office likes to point its finger at Luxembourg and the Cayman Islands for sheltering tax cheats. But according to the U.K.-based Tax Justice Network, the United States is the biggest tax shelter of 'em all, thanks to the great state of Delaware. Delaware, says the Tax Justice Network, is "the most secretive financial jurisdiction in the world." That's based on an analysis of 60 financial jurisdictions according to level of secrecy and cooperation with foreign tax authorities.