An interesting article presents results of an investigation into usage of .NET on five versions of Windows XP and Windows Vista.
It's quite surprising to see that Microsoft intended to use .NET framework as an important constituent of the Longhorn (Vista) operating system.
"One of the most important things when you think about Longhorn is, it's not just another operating system release like Windows XP or Windows 2000. We think about it more like a wave, and the wave is really made up of more than just any one particular thing. Think about the wave being built upon a foundation of a new platform investment that we've made across the board, built on top of the .NET foundation. And then with Longhorn there'll be client releases and a server release." (Michael Wallent, general manager of the Avalon team, 2003)
Last pre-beta 2 build of Windows Vista (5308) has only 27 managed files (.NET files) and 2464 unmanaged executable files. Microsoft built very few applications in .NET (for example Windows Server Update Services) and doesn't intend to include in its OS a famous .NET application written by a Microsoft employee: Paint .NET.
After an insightful analysis, Richard Grimes concludes that "Microsoft has lost its confidence in .NET. They implement very little of their own code using .NET. The framework is provided as part of the operating system, but this is so that code written by third party developers can run on Vista without the large download of the framework."