1. A computer-implemented method for enabling content providers to provide targeted content to users, the method comprising: generating a database that maps specific IP addresses to specific behavioral segments, said mapping derived from behavioral data collected from each of a plurality of Internet Service Providers (ISP), said behavioral data including information collected by the ISPs regarding Internet access activities of their respective subscribers, said behavioral segments reflecting subscriber interests; and providing content providers access to the database via a query interface, said query interface configured to receive a request that identifies an IP address, and to look up from the database and return information identifying one or more behavioral segments corresponding to the IP address, wherein the query interface is further configured to return the information by at least: determining whether the IP address can be mapped to a subscriber-specific behavioral segment that is specific to, and based on Internet access activity of, an ISP subscriber associated with the IP address; when the IP address can be mapped to said subscriber-specific behavioral segment, returning, via the query interface and in response to the request, an identifier of the subscriber-specific behavioral segment and when the IP address cannot be mapped to a subscriber-specific behavioral segment, returning, via the query interface and in response to the request, an identifier of a region-specific segment that reflects user preferences associated with a geographic region corresponding to the IP address, wherein the method is performed by a computing system comprising one or more computing devices.