Windows Workflow and scalability

There is an interesting thread on the MSDN forums about WWF Scalability.  The question was how many concurrent workflows can a single workflow instance handle.  The answer was the number of .net threads available to the process the workflow runtime is hosted in.  Which appearently is around 25 for a single proc box and 100 for dual.  According to Srikanth there is even a value on the constructor of the DefaultWorkflowScheduler object, which recommended value for which is 20 on a single proc box.

This raised some issues of scalability by some people; however, I think that prudent use of the persistence service and handling long running operations outside of the workflow will allow WWF to scale well enough.