There has been a lot said about WS-Context over the years, most recently at the W3C workshop on Web of Services and in the majority it has drawn positive comments. In summary, WS-Context defines a basic (extensible) context structure that can be associated with an abstract activity: the lifetime of the activity is the lifetime of the context. The activity can then be used to model a session: all interactions on a session-oriented service in the scope of an activity will be uniquely and unambiguously tied to that activity through the context. Importantly, the context (and hence session) is not tied to the endpoint reference of the service: the same service can be addressed by multiple clients or services in the scope of different sessions concurrently. The session concept is therefore loosely coupled with respect to communication channels and service endpoints: the session may be used in conjunction with a service for a short period or even shared across multiple services. Late binding also means that protocols may use WS-Context to support either ephemeral or long-lived sessions associated with a fixed service endpoint definition as appropriate within an application.
Although there may appear to be overlaps with WS-Addressing, the two are more complimentary than competitive. Think of the possible relationship like URIs and cookies in the traditional Web. If used together and used right, loosely coupled, scalable stateful and stateless interactions in Web Services are possible. If used incorrectly, or ignored then closely coupled, brittle systems can result. Whether WS-Context has a big impact on the evolving Web Services architecture remains to be seen. The fact that IBM and Microsoft were not involved will certainly hinder the take-up and influence.