Rachel Maddow did a great bit on this last year --
"Here comes the 'Let‘s take a trip to the Cayman Islands' part of our program. What you see here is an address in the Cayman Islands listed as Ugland House. It is a five-story building home to 18,887 businesses—or I should say, it‘s home to the fake headquarters of 18,857 companies that want to look like they‘re headquartered there in order to avoid paying taxes somewhere else. If there really were 18,857 businesses there, don‘t you think the parking lot would be a little bigger?
.......
Stopping U.S. companies from not paying taxes on their profits overseas, closing that loophole would bring in about $21 billion in tax revenue each year—revenue that is owed but is not being paid because of scams like the 18,000 companies in that one building in the Ugland House.
The Republican Party has decided to come down on their side, remarkably. They have decided to come down on the side of the scam, pitting their political future on fighting for the rights of American companies to avoid paying taxes in America. Like individual Americans do."
http://www.msnbc.msn.com/id/30641410/ns/msnbc_tv-rachel_maddow_show/