The book is a MUST READ for all .NET developers and provides an insight on .NET Framework 4.0 that includes Framework Class Libraries (FCL) as well as Common Language Runtime (CLR).
“Dig deep and master the intricacies of the common language runtime (CLR) and the .NET Framework 4.0. Written by a highly regarded programming expert and consultant to the Microsoft® .NET team, this guide is ideal for developers building any kind of application-including Microsoft® ASP.NET, Windows® Forms, Microsoft® SQL Server®, Web services, and console applications. You’ll get hands-on instruction and extensive C# code samples to help you tackle the tough topics and develop high-performance applications.”
Also check out Jeffrey’s blog on what’s new in 3rd edition. I’m really enjoying reading the book and recommend all of .NET folks out there to read that book for better understanding of CLR and FCL.