My colleague Jeroen pointed me to this 2006
article on WS-RM by Clemens Vasters of Microsoft. An excerpt:
Truth be told, the reliability of WCF's WS-ReliableMessaging-based implementation by itself is "only" as good as it can be for a volatile reliable messaging mechanism
...
If you need end-to-end durable reliable messaging with full support for transactional I/O you need an infrastructure that's in control of both ends of the communication path and as it happens, such an infrastructure is part of the Windows operating system family. If these are your requirements, your WCF binding of choice is likely the NetMsmqBinding.So let me repeat it again: if you don't want to loose messages, use a prorprietary messaging solution (e.g. MSMQ) or use a B2B protocol such as AS2. Or use AMQP once it gets some traction and is supported by larger IT players. Microsoft
joined the AMQP working group in Oct. 2008. If Microsoft would release an AMQP implementation with WCF binding, that would be headline news!