I am thrilled to write about this new technique that I discovered only some days ago. While I have been using .NET Reflector since many years ago to disassemble .NET and Visual Studio assemblies to understand how they work, until now I had to use my brain as debugger when trying to figure out things.
Some time ago Microsoft provided a way to debug assemblies of the .NET Framework. With the .NET Reflector tool (VSPro edition) and the approach presented here, you can debug Visual Studio assemblies too. In the sample provided, you can debug the installation of an extension through the Extension Manager of Visual Studio:
HOWTO: Debug Visual Studio assemblies with .NET Reflector.