Google is experimenting with chaging the ads it displays to individual users based on their behavior — e.g., which ads they choose to view. ClickZ news reports:
Google confirmed Friday it is indeed tinkering its premium AdWords positioning based on user clicks — or the lack thereof. Explained Google spokesperson Michael Mayzel, “In this instance, we are exploring changes to the way we promote ads to the top of the search page. This is designed to further ensure that users will find ads only when they’re most useful and advertisers will receive the most qualified leads. With this improvement, users may see more prominent ads if they are currently showing interest in ads and less prominent ads otherwise.”
I was not able to duplicate the example described in the article, but this is an obvious thing for Google to do. Within a session, and across sessions if you log in, Google knows what ads you have viewed. It makes sense to replace ads you don’t seem interested in with new ones. With all of the data Google can collect it is also possible to build up both user specific and generic profiles — user timFinin is just not interested in Macintosh related products; users who seem interested in Canon digital cameras are also interested in Nikon digital camers but not Casio cameras.