10. The computer implemented method of claim 7 , wherein the act of serving the first document in association with ads relevant to the second topic includes scoring ads relevant to the second topic in response to the receipt of the information, and serving the ads relevant to the second topic based on their scores.
7. A computer-implemented method comprising: a) providing, by a computer system having at least one computer in a network, a first document, the first document including 1) content concerning a first topic, and 2) a link to a second document including content concerning a second topic; b) serving, by the computer system, the first document in association with ads relevant to the first topic; c) receiving, by the computer system, information indicating that a user selected the link; and d) responsive to the information and further information indicating that the user navigated back to the first document after having navigated to the second document, serving, by the computer system, the first document in association with ads relevant to the second topic, wherein the ads relevant to the first topic are different from the ads relevant to the second topic.