Steve Maine writes about his eureka moment with the WS-Addressing spec.  The basic ideas behind it is that it's a good idea to write the address (e.g. put the address in the SOAP headers) on the front of an envelope rather than only writing the name on the envelope and telling the postman the address (e.g. leaving some address information in the SOAP envelope and some on the transport protocol headers).

The other useful aspect of the WS-Addressing spec is the idea of the <wsa:EndpointReference>.  This is an XML node that can contain any information a client or server require.  It's like a cookie mechanism for SOAP messages.  Omri talks more about it and shows how it's useful in WS-Eventing.  Omri refers to the 'resource model' that WS-Addressing provides:

The idea is that the organization of resources behind a Web service is opaque to the caller.  There can be a single resource that "fronts" for a bunch of other resources - which in turn can be organized hierarchically, scaled out, or employ whatever internal organization is appropriate.  The caller does not (in fact should not) need to know about this internal organization. 

I think this use of a front-controller style pattern is another of the ideas that excited Steve.  Don Box also talks this when he says that WS-Addressing is a solution to URI manipulation.  Instead of having to use querystrings to indicate what should be done at the receiving end, this information can be sent through with the EndpointReference.