There's a great article over on DevX that covers the Stream and Formatter architectures. It does so from a VB.NET point of view, which is fine because the article is attempting to teach people converting from VB6- to VB.NET to move away from the proprietary VB file operations. In general, the article is generic enough that the knowledge is applicable in all languages and is definitely worth the read.

There's a new .NET show online over at MSDN. This one is about understanding the design of the framework class libraries. Here's a quick summary ripped straight from the site:

One of the most common issues that I hear from programmers who are beginning to use .NET for developing their applications is that they are having some problems understanding the structure and layout of the .NET Framework and the features that it supplies. So I thought it might be a good idea to take a look at the "object model" of the .NET Framework and hopefully give you a better understanding of how it is organized.