Source (Dutch): Tweakers.net

When you search with Google not only organic results are shown but also a number of sponsored links. Which sponsored links to show is based on the search terms entered by the user, until now.

Google is also going to use the profile of each individual user to define which sponsored links to show. This profile is based on the cookies stored on the users PC. A similiar technique is already being used by Yahoo and AOL.

Google is however going to offer users the possiblity to make modifications to their profile. This way people can specify which advertisements they're interested in.