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
I used Windows Workflow in a web application designed to manage the lifecycle of change control requests in an enterprise system. I admittedly fumbled around in it, and definitely didn't do a lot of things correctly, but it worked pretty well and I was satisfied with how easily I could change the rules without writing even more code.
However, once I rolled off the project, the person who inherited it decided he didn't like WF or didn't want to learn it, so the application died and they went back to using emails and phone calls. So the the implementation was successful, but the investment was ultimately a waste.