1. A computer-implemented method comprising: a) accepting, with a computer system including at least one computer, ad scores, wherein each of the ad scores indicates a value of a user selection of an ad; b) scoring, with the computer system, a document using ad scores of the ads when the ads are served with the document and ad scores of the ads when the ads are served across a collection of documents to generate a document score; c) accepting, with the computer system, a cost for an action with respect to an ad when the ad is served with the document; d) adjusting, with the computer system, the cost using the document score to generate a modified cost; and e) billing, with the computer system, an advertiser associated with the ad, using the modified cost.
1. A computer-implemented method comprising: a) accepting, with a computer system including at least one computer, ad scores, wherein each of the ad scores indicates a value of a user selection of an ad; b) scoring, with the computer system, a document using ad scores of the ads when the ads are served with the document and ad scores of the ads when the ads are served across a collection of documents to generate a document score; c) accepting, with the computer system, a cost for an action with respect to an ad when the ad is served with the document; d) adjusting, with the computer system, the cost using the document score to generate a modified cost; and e) billing, with the computer system, an advertiser associated with the ad, using the modified cost. 2. The computer-implemented method of claim 1 wherein each of the ad scores indicates a conversion rate of an ad.