If you are looking for information on how to troubleshoot a variety of IIS-related issues, the following week of Webcasts from Microsoft.com OPS team is not to be missed. Mark your calendars!
Of course, these sessions focus on issues AFTER you have determined that your problem is NOT with invalid configuration but with something running awry on the server. I know, I know, distinguishing misconfiguration from buggy code is not easy, but there are tools like DebugDiag and general troubleshooting steps/guidelines to help you. And if you need help with diagnosis, post the IIS State or DebugDiag log file with a clear subject line to the microsoft.public.inetserver.iis newsgroup on msnews.microsoft.com for assistance.
I consider Microsoft.com one of the closest and best customers of IIS... because they have an incredibly seasoned and talented OPS team (former IIS can't hurt...), which allows them to be on the bleeding edge and be the first and largest consumer of beta IIS builds. As a result, they have unbelievably intimate access to the IIS product developers when it comes to debugging or feature suggestions, and they are privy to a variety of internal details and conversations you simply won't find anywhere else.
Let's just say that they definitely do their homework on issues and bring a wealth of experience to the table. I am hard pressed to name another group of people of comparable skill and experience when it comes to IIS and operations.
So... I suggest listening to what they have to say about debugging IIS. But, don't just take my word for it; see it for yourself. :-)