1. A system for dynamically generating web pages, comprising: a plurality of content services that are responsive to service requests by returning content; and a web server machine that retrieves content from the content services via service requests, and uses the retrieved content to dynamically generate requested web pages, said web server machine programmed to respond to a request from a user computing device for a dynamically generated page by retrieving predictive information regarding content likely to be used to generate the requested page, 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 page generation events.