Two companies based in California, Adisn and Tumri, are experimenting with new strategies for online ads. They are creating “hundreds of versions” of online ads with different fonts, images, colors, etc., in an attempt to see what visuals work best. After studying the online behavior of users, they will attempt to tailor the ad to what the system believes the user is interested in.
http://www.nytimes.com/2008/12/03/business/media/03adco.html?ref=media