Avoiding the '401 Unauthorized' Error when Using the ReportViewer

ASP.NET 2.0 includes a new control for viewing Reporting Services reports within your web application - without having to navigate to the ugly (and cumbersome) Reporting Services web UI. However I found that using it in production is a bit trickier than using it on your development machine. Read on for a Gotcha' that took too many hours of my life.