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 page requests from user computers by preemptively sending selected service requests to the content services to prefetch content deemed likely to be used to generate the requested web pages.