Washington’s Blog 
Wednesday, May 6, 2009
Enron was lambasted for using offshore tax havens  and complicated corporate structures to avoid paying taxes.
But the big banks are worse.
As the Financial Times notes :
In recent separate surveys by the US Government Accountability Office and the Tax Justice Network, the largest user of tax havens in every country surveyed was a bank. Tax authorities have enormous problems puzzling out these structures. If they can, it is often hard to characterise them as shams.