1. A system for dynamically generating content, comprising: a plurality of content services that are responsive to service requests by returning content; and a server machine that retrieves content from the content services via service requests, and uses the retrieved content to dynamically generate responses to content requests received over a network, said server machine configured to respond to a content request received over a network from a computing device by retrieving predictive information regarding content likely to be used to generate a response to the content request, and by using the predictive information to preemptively request, via one or more service requests to one or more of the content services, at least some of said content that is likely to be used, said predictive information based on past response generation events.