Improving .NET Application Performance and Scalability
This series can still be found here:
While some of the content is stale since it refers specifically to .NET 2.0 I think all of the conceptual content broadly applicable (even beyond managed code systems to software systems generally.)
If you're looking for it some time in the future you can find it again easily with bing. I doubt that they'll get rid of it entirely for a very long time.