Cory Doctrow is a huge advocate of the open source software movement. He went further when he released his first book, Down and Out in the Magic Kingdom, for free under a Creative Commons license. His rational is quite simple: obscurity is the worst enemy of an author, so get it out in whatever form you can! The more people know and talk about your work, the more will buy it, and apparently this model works well for him.
He's written several books and a collection or two of short stories, most of which are available for free off of his web site. Because of the license that he uses, they've also been translated into a number of languages and eBook formats, I currently have two of his books loaded on my iPod Touch -- Magic Kingdom and Eastern Standard Tribe.