Do HiveMind & Co. provide stateful services? I don't think so. Should they? As I'm growing increasingly fond of the Hibernate long-session-pattern, I do think so. You'd probably need some means of attaching/detaching some client-id to a thread (a servlet-filter, typically), so, after that the container could maintain same (service-id, client-id) to service-implementation map. In the servlet-case parallel request from the same client could be blocked (synchronised on) - actually this should be the general case - clients wanting to be served concurrently must provide thread id's instead of client ids.
HiveMind's pooled services should already be quite close, only, the pool needs to become aware of the client-id's -- I need to have a look at them.