I just saw this while looking around for something else - IBM published a paper in late September on the XMS client library for their MQ brokers. I posted about this previously. Essentially this is a .NET client for their MQ brokers, including an implementation of some stuff from JMS. That means publish/subscribe capability, partly. The new article offers some new info and clarifies a few things for me. Specifically, when IBM says "MQ Brokers", they include the regular MQSeries in that. Since CSD08 of MQ V5.3, IBM has offered a pub/sub capability in the base MQ. So this XMS stuff works with that. (IBM are now up to v6.0 of MQ.)
A nice interoperability option! This fixes the JMS-is-not-interoperable issue I had raised previously.
Remember, the .NET client library for plain-old-MQ is a separate thing - that has been a part of IBM's MQ product since MQ5.3 CSD05. But, what this XMS thing is, is a pub/sub client. Something a little different.