1. A storage device having instructions stored thereon, the instructions, when executed by one or more processors, cause the processors to perform operations comprising: a) accepting IP address usage information associating various IP addresses with various client identifiers; and b) generating an estimate of a number of users for at least one of the IP addresses using the IP address usage information, wherein the client identifiers include cookies, and wherein the act of generating an estimate of a number of users for at least one of the IP addresses comprises: i) determining a number of cookies for the at least one IP address for a given period of time producing a first ratio, and ii) multiplying the first ratio by a second, predetermined, ratio of a number of users per cookie for the given time period.