.NET Reflector lets you follow bugs through your own code, 3rd party components, and any compiled .NET code you work with. You can see 3rd party code in Visual Studio, and debug into it just like your own. Go to the definition of compiled code (F12), set breakpoints (F9), and step into it (F11). You can see how data flows through a library or component, and watch locals change as you debug, find dependencies, and track down the exact location of bugs and performance issues.