1. A web site system, comprising: a web server system that is responsive to requests from online users by generating and returning web pages, wherein the web server system includes one or more applications the generate personalized content for recognized users based on browse histories of such users; and an event history server that persistently stores event data descriptive of events that occur during browsing sessions of each of a plurality of users of the web server system, and makes such event data available in real time to the one or more applications to facilitate personalization of web pages for the users; wherein the event history server implements a query interface through which the one or more applications can retrieve the event data of a given user by event type and by event time of occurrence.