I've had bad luck with Haskell's laziness causing hard to debug performance issues. Also the lack of libraries really hurts when it comes to even basics like queue and database interactions. Many times there's a few libraries that are all half finished. Don't get me wrong, I really like Haskell a lot, I just find that F# brings a lot of well-thought out compromise between Haskell and the wealth of libraries in .NET for production code. If it was my money in my startup, I'd have no qualms betting on F# to get me to market as soon as possible. If it was my personal OSS project that I work on for personal edification and enrichment, I'd choose Haskell nearly every time.