[While Luke Wroblewski was writing his well-received book, Web Form Design: Filling in the Blanks, he asked if I could think of an example where a change in a form's design made a noticeable difference in business. "You mean like $300 million of new revenue?" I responded. "Yes, like that." said Luke. So I wrote this article, which he published in his book.]
read How Changing a Button Increased a Site's Annual Revenues by $300 Million ?