I'd love to use C# or F# for development: they're in my opinion, superior languages to Java and Scala (respectively) -- although Scala has several salient and interesting points (implicits, traits) that F# doesn't. However, I am fairly well wed to Linux/OS X, and don't see myself being productive with Windows (whenever I used Windows, the first application I'd install is Cygwin), nor (having never done Windows System…
You don't really need Windows to write C#, F#, etc. There are emacs modes for them if you like emacs. I'm pretty sure there's an F# module for Monodevelop available.
It doesn't help you with the OS situation at all, but Visual Studio express is free from Microsoft should you find yourself on Windows.
I know C# better than most of the other languages in my toolkit, and it's pretty great, but I don't think that Windows is very enjoyable to use when compared to an OS with unixy underpinnings. Should you decide to check out C# or F# in more depth, I'd recommend staying on the OS you prefer.
Mono is production quality today, you don't have to wait for it.