If I'm right the new StateMachine uses WCF as communication mechanism between the host and the running workflow.
Why did you replace the eventing stuff with WCF ?
I'm using the 3.0 StateMachine at the client side (WinForms) in order to flow a wizard.
Using WCF would mean creating a ServiceHost on the client which looks heavy to me.
Moreover it will create more work in order to migrate to 4.0
It would be nice to have the choice between WCF and events.