As a programmer, I feel much safer knowing that the frameworks being 'sold' to me are actually in use by their creators to produce real applications, as this gives me some reassurance that they will actually solve some set of problems, and are not just architecture astronautics.
I remember years ago in the days of .NET 1.0 and 1.1, there was a lot of hype about how the next version of windows (which would have been Vista) was going to make heavy use of .NET, and there lots of hype about how great that would be.
I remember at the time thinking "well if Microsoft are basing their products off it, it must be pretty good." However, that didn't actually happen, and Vista ended up containing almost zero .NET parts. I also haven't heard of them using it in any apps that they sell at all (except IIS)
Although I've had many great experiences with .NET myself, the fact that Microsoft don't appear to use it themselves hardly fills me with confidence. In contrast, all of the frameworks Apple ships in OSX such as CoreData are all in heavy use by their major apps...
Off the top of my head I know of these 'purchaseable' MS apps which use .NET:
- IIS7
- Visual Studio (which I don't think really counts...)
Are there any others?
Disclaimer: I believe this is programming related, as it deeply affects the confidence that I as a programmer have in a technology, and counts a lot when evaluating what to use when building my next apps.
I would feel equally compelled to ask the same question again about a subset of .NET, such as WPF or WCF, or any other native win32 library, before deciding to write any apps using it...