I wrote the software behind SnapAds. Before that I wrote an optimizer service for web pages that operates on HTML, CSS or Javascript. Check it out at http://demo.genetify.com .
Let me know if there is any interest -- I'd like to open-source the project.
landing pages for user signups,
homepages for media websites (nytimes and other big blogs),
email campaigns,
product promotions and offers or even defining pricing if you do a saas company
as a point of clarification, the system greg's built goes much further than simple a/b testing. there are quite a few complications with implementing a genetic algorithm in the real world of constantly shifting preferences.
once done right, it can efficiently optimize millions of permutations with millions of ad impressions (<2000 clicks). more permutations means more chance for improvement, and this just isn't possible with a simple a/b testing solution.
Headlines? The images that accompany news stories?