I have recently posted a question regarding the Windows Workflow running in a web application. Granted it was a fairly technical question that contained terms like ManualWorkflo
We use the state machine workflow to manage a couple service request processes with about 10 states each. I am not sure if it is was 100% the right choice, because implementing a simple state machine design would have been simpler(maybe we suffered here from BDUF).
The biggest downside for us was the learning curve. I mean, workflow is practically a stripped down version of biztalk(for free!).
Off the top of my head, these are the areas we've benefited from WF:
I always try to keep in mind that it really is a foundation. As a developer/architect, you have to commit to building something useful on top of it.