WF 4.0 State machine workflow

Recently, I have been working on WF 4.0. On the look of it Workflow Foundation looks pretty impressive. The XAML based designer for developing the workflow is pretty responsive. I got a chance to evaluate State Machine workflow and did manage a quick Proof of Concept within just a day or two. The persistence and tracking capabilities with SQL Server are good and robust. However, not support for Oracle persistence which means develop you own custom instance store to persist long running workflows. Hmmm.. something not very impressive ... It is light and performance of WF 4.0 is 10 times faster than that of WF 3.0. However, there are few concerns around testability of XAML based workflow and also maintainability. One needs to carefully devise a strategy to migrate the existing workflow instances when a workflow undergoes a version change. It has decent support for transactions, exception handling and bookmarking. Overall I am pleased with what is on the plate!