I realize that there is probably great documentation for other open source frameworks as well, but I can see that it's likely Microsoft will always have great documentation on the very latest versions of their tools as they pay people to make the documentation, whereas OSS frameworks are more likely to rely on people to write boring documentation in their spare time.
Examples: Tons of free video tutorials: http://www.asp.net/web-forms http://www.asp.net/mvc http://www.mvcconf.com/
heaps of books http://www.asp.net/community/books http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Dap...
then of course there is the Microsoft Developer Network http://msdn.microsoft.com/en-au/ff380144
with training courses/hands on labs http://msdn.microsoft.com/en-au/VS2010TrainingCourse_AspNetM...
plenty of people who can answer your questions on SO (C# and ASP.NET are a couple of the most popular tags) http://stackoverflow.com/tags
and msdn forums http://social.msdn.microsoft.com/Forums/en-au/categories
if you want to pay for training, there's plenty of that too, as .NET is used lots in the enterprise there is training centres and other paid services a plenty: http://www.learnvisualstudio.net/ http://learning.microsoft.com/manager/catalog.aspx?brand=msd...
additionally, they have a certification program with all the training materials and training courses for that http://www.microsoft.com/learning/en/us/certification/cert-v...
I realize that there is probably great documentation for other open source frameworks as well, but I can see that it's likely Microsoft will always have great documentation on the very latest versions of their tools as they pay people to make the documentation, whereas OSS frameworks are more likely to rely on people to write boring documentation in their spare time.