These days, fuzzing is most frequently used to validate file and network parsers - literally piping a random source of binary data into the parser and then seeing what happens.
In the November issue of MSDN Magazine, Dan Griffin takes a look at the extensibility of Visual Studio 2005 Team Edition for Software Testers and creates a Test Interface Provider (TIP) that implements a fuzz testing strategy.
Explore the sample code online, or grab the code download to explore on your computer.
Also, take a look at the Visual Studio Extensibility Developer Center for additional resources to help you create the best development environment for your projects. You'll find more articles, downloads, videos, webcasts, and links to helpful developer blogs.