I'm coding my startup in F# and I love it -- I don't ever want to go back to C# or any of the other .NET languages.<p>The cool part isn't just the FP, the cool part is how you can suck in all the other libraries written in .NET and use them easily.<p>If mono supported tail-recursion optimization I'd go there in a heartbeat, but I'm very, very happy with F# and a stripped-down MS stack. Plus as long as I don't start writing aspx pages (and I'm not!) and keep my separation of concerns, I can easily move to a *nix environment at some later date.<p>I'd encourage you to check out F# some more. I had a hard time coming from an imperative background, but eventually it started clicking.