I'm using Windows Workflow Foundation and WCF for some weeks now. More specifically I'm using .NET 3.5 and Orcas Beta March 2007 CTP. These things are kind of complex beasts. I don't know how adoption will go. Microsoft appeals to the visual developer who may not have a theoretical foundation to fully understand what the machine is doing.
My main frustration with Orcas and WCF is how the clients generated are different from the original service! The client generated in fact does not implement any of the interfaces I defined for it. How can I pass data and interact with the service if there's a fundamental type mismatch betwen client and service? In WF persistence, for instance, I mark my server class as serializeable. Guess what: the client is not serializeable and therefore the workflow can't be persisted!
Some day I'll compare the fundamental differences of frameworks and tools between .NET and Java here.