Required reading on multithreading.
Vance Morrison, who is the compiler architect for the .NET runtime, wrote a great article on multithreading for the August issues of MSDN Magazine. You might read MSDN Mag regularly anyway, as you should, but this article is worth calling out.
I've worked on applications that sparingly used multithreading (mostly to kick off background threads for long-running procedures, and (of course) for UI stuff), but have not had the opportunity to work on enterprise-level multithreaded apps before. Like most developers, I've tinkered with the samples and worked out the possibilities. But working in the environment that I do, most of our stuff is single-threaded.
However, I had aleady identified multithreading as something to concentrate on in my next phase of personal development. And then I ran across this article.
If you're interested, this article will get you on your way to the next level of code mastery. I consider it required reading.