It’s in the very early stages of its development, but I just found a new site called Booklamp, which claims to do for books what pandora.com (sadly, off limits to us) does for music: recognize patterns in the ones you like and suggest others that you might as well. The FAQ is not available yet to shed some light on how the matching is done, but it seems to employ five criteria: “density”, “pacing”, “action”, “dialogue” and “description”.
There are very few books in the database yet, so it’s more of a novelty than a useful tool, but they claim to be adding more. I wonder how they’re ever going to compete with Amazon’s massive catalogue and years of actual data about people’s taste in books.
The site’s administrator seems to have a sense of humour as well: I picked the first immediately recognizable book on the list, 1984 by George Orwell, and asked it to find me some matches. The first listing was the USA Patriot Act.