1. A web site system, comprising: a web server system that is responsive to requests from online users by generating and returning web pages, said web server system comprising one or more machines, and comprising one or more applications that 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, wherein the event history server stores the event data substantially as corresponding events are reported to the event history server by 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 retrieve the event data associated with particular users at least by event type and event time of occurrence, and the event history server is capable of responding to a query submitted by an application via said query interface by identifying particular events that match event criteria included in said query, and by returning the event data for said particular events; wherein the event history server records the event data for a given event as an event object, each event object being separately retrievable via said query interface; and wherein the web server system uses the event data retrieved by the one or more applications via said query interface to generate personalized web pages for transmission to users.