6. A computer-readable memory device comprising: a plurality of instructions which, when executed by one or more processors, cause the one or more processors to: determine a rate of appearance, a rate of disappearance, or a rate of update of advertisements within a document over time; determine a measure of quality of advertisers associated with the advertisements within the document, where the measure of quality is based on: an amount of traffic to, or a measure of trustworthiness of, advertising documents referred to by the advertisements; generate a score for the document based on: the rate of appearance, the rate of disappearance, or the rate of update of the advertisements within the document over time, and the measure of quality of the advertisers associated with the advertisements; rank the document with regard to at least one other document based on the generated score; and present, based on a search query, the document and the at least one other document, where the document and the at least one other document are presented in an order that is based on the ranking.
6. A computer-readable memory device comprising: a plurality of instructions which, when executed by one or more processors, cause the one or more processors to: determine a rate of appearance, a rate of disappearance, or a rate of update of advertisements within a document over time; determine a measure of quality of advertisers associated with the advertisements within the document, where the measure of quality is based on: an amount of traffic to, or a measure of trustworthiness of, advertising documents referred to by the advertisements; generate a score for the document based on: the rate of appearance, the rate of disappearance, or the rate of update of the advertisements within the document over time, and the measure of quality of the advertisers associated with the advertisements; rank the document with regard to at least one other document based on the generated score; and present, based on a search query, the document and the at least one other document, where the document and the at least one other document are presented in an order that is based on the ranking. 7. The computer-readable memory device of claim 6 , where the plurality of instructions further cause the one or more processors to: determine an amount of traffic that the advertisements generate to advertising documents referred to by the advertisements; and where the plurality of instructions, which cause the one or more processors to generate the score for the document, further cause the one or more processors to generate the score for the document further based on the amount of traffic that the advertisements generate to the advertising documents.