Tess is a PSS escalation engineer for Microsoft and she has a really priceless set of blog posts on using some of the more advanced debugging tools that ship with .NET to better understand what is happening when things go wrong on the server (memory leaks, deadlocks, crashes, etc), identify root causes of issues in apps, and how to fix things.
Here are a few of the great posts she has done recently:
I really want to thank the awesome PSS team we have all around the world that support ASP.NET and .NET. As you can tell from the above articles, they have an absolute ton of knowledge, and need the skills to help diagnose and fix what is going on in a remote process full of customer app-code they've never seen.
Julia Lerman recently posted a nice blog entry about her first Microsoft PSS support call experience (on a holiday) that is worth reading if you have never called before. They can be a real lifesaver if you ever get stuck or are having a problem that you just can't figure out on a deadline.
Hope this helps,