That MS hasn't written parts of the base OS in .NET is no way in my opinion a reflection of their support of .NET, every language/platform has its place. Personally I want everything in the OS to be as fast and as small as possible, this is not what .NET does the best.
Now if they were to rewrite calculator, notepad, and all the other collection of 'apps' in .NET I would be impressed, but honestly why invest the man hours when they have a proven codebase that has been heavily tested and debugged?
.NET is GREAT for writting business applications, from Web Services, to day to day applications, and this is where it should be used in my opinion.
John