I'd like to drill down on this issue, because  to me it seems a rare technical question amongst a sea of WS-FUD.  Tony has presented the case in abstract.  DAIS raised a concrete example some months ago. 

The question, as I understand it, is how to send a single message to multiple resources held by a given service using WSRF.  (The supposition is that you know that these resources are accessible via the same service).  I've had two possible patterns suggested to me that address this question :

1.  Pass multiple EPRs to an operation on the service

2.  Use a service group

To take these in turn, the first pattern is worth highlighting because some  critics of WSRF assume that the only way to use an EPR is to call an operation on it directly.  Of course this isn't true; you can actually pass EPRs as arguments to another operation if that suits your needs.

The second pattern provides a single operation on a group of resources.   At first glance this seems to have the downside  that the server controls which resources are in the set, rather than the client passing in a list.   However, Ian's comment above suggests that the service group can provide a mechanism that allows operations to be invoked on subsets of the resources.  I don't know enough about service groups to comment, except that this seems a reasonable solution.  

I would appreciate seeing these patterns explored in more depth  - possibly in a face to face meeting next week?  From the above, it certainly seems that the technical concern that Tony articulated can be addressed.