He created Google Adwords campaigns for several possible titles, including "Broadband and White Sand," "Millionaire Chameleon," and "The 4-Hour Workweek." By running each of these campaigns on Google for a week and seeing which title attracted the most click-throughs, he determined that "The 4-Hour Workweek" was a potential winner. He published the book with that title, and it went on to be a major bestseller.
Cost of this research program? $200.
In book publishing, we tend to assume that success is a matter either of luck or of sheer ineffable instinct, which you either have or you don't. Stories like this suggest to me that we could probably achieve success a lot more often if we used our ingenuity to find ways of pre-testing our ideas.