Use Conversions To Generate More Conversions | How-To | Smashing Magazine
http://www.smashingmagazine.com/2009/05/23/optimizing-conversion-rates-less-effort-more-customers/

a technique that uses information collected on an individual’s web-browsing behavior, such as the pages they have visited or the searches they have made, to select which advertisements to display to that customers.

I liked this article - particularly as Rob and I were looking at the washington post site for other reasons earlier

Send examples of links and buttons that interrupt a website visitor's ability to take an action, specifically "nuke" buttons that kill conversions. Post the URL in the comments area of this blog, or send a screen shot by email to http://www.conversion-rate-experts.com/contact-us/. For instance, why would a "Clear Form" button be next to a "Place Order" button? Does the website owner want visitors to cancel the order accidentally? Or how about buttons with drop down menus that get in the way when a visitor is trying to fill in a search box? Does the website owner want visitors to click away from that page by accident instead of searching the site? Let's see a collection of these bloopers.