Here are links to two videos explaining the Financial Secrecy Index (not the same as tax havens, necessarily, though there is a lot of overlap) and how the US/Delaware tops the list.

http://taxjustice.blogspot.com/2009/11/blog-post.html

http://taxjustice.blogspot.com/2009/11/financial-secrecy-index-usa-tops.html

Enjoy!