In a recent conversation with a writer, we were discussing the Internet, and the writer mentioned how he was posting some of his unpublished book manuscript online for people to read. This was not the first time I'd talked to a writer who had this idea.
Though something like this may seem like a good plan—especially if you're actively looking for advice and/or feedback—posting material from an unpublished book on the Internet is a big no-no if you still want to sell the book.
First of all, as detailed in a previous post on copyrights, you're inviting other writers to steal your idea. Secondly, posting material online makes it less valuable to publishers, and therefore, less attractive to agents. Material that's available online for free is less probable to sell, hence agents' hesitancy taking on such projects.
Perhaps your goal is to put good material online in the hopes that someone such as an agent or editor will come across the site and contact you. Unfortunately, the odds of this are very, very low. If you really are looking to get your work noticed by agents without going through the traditional submission process, my best advice is to get short stories published in prominent journals, or get your nonfiction articles published in prominent magazines. Agents read those publications, and they sometimes contact writers out of the blue and say something along the lines of, "I enjoyed your article in Prominent Magazine. Do you have representation? Have you ever considered writing a book-length manuscript?"
And that's when you say, "Well ... funny you mention it, because..."