Furthermore, in general F# seems to generate far less efficient code than C# does, and for the kind of development I do (games/multimedia) I'm not really willing to sacrifice even more performance just because some FP fanatic thinks C# should go away. Personally, I think the C# compiler and the .NET JIT should have a lot more tuning applied, and get things like SIMD introduced, but MS doesn't seem to care about that.
Writing code in C# also makes it accessible to a much wider set of developers. The overlap and shared heritage with languages like Java is definitely a plus, even if I don't like some of the shitty design baggage that comes with it. It's already a struggle to get the community engaged with my project, JSIL - if it was written in an obscure language like F#, it'd be nearly impossible.