1. A computerized event distribution system, comprising: a source of event messages; a plurality of matchers for determining whether received ones of the event messages fall within an event message scope defined by each of a set of hosted subscriptions and issuing corresponding notification messages to corresponding subscriber clients; and at least one event message router communicatively coupled to the source of event messages and programmed to selectively pass event messages to the plurality of matchers, and wherein the at least one event message router is capable of maintaining, for each one of the plurality of matchers, an imprecise summary of subscriptions for which each of the plurality of matchers is responsible.