A couple of IBMers who help develop the messaging components in WebSphere products have their own blog.
The WebSphere and Messaging blog discusses WAS and messaging, specifically components like the service integration bus. Topics include the new Cluster Bus Member Wizard in WAS 7, getting XA recovery working in a bus, and how to connect multiple SIBuses. For an overview, see WebSphere Application Server V7.0 Messaging. This is obviously pretty deep technical stuff, not just marketing. I hope you'll find it useful.
These guys also contribute to the WebSphere Community Blog, which isn't so specifically focused on messaging but on WebSphere products in general.