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.

If I had to pick one single advantage of F# over Haskell, it would be the general lack of partial functions. F# also does some really neat things with pattern matching. (See, for example, active patterns.)

The C#-style object model is arguably an advantage for certain purposes. I always feel guilty doing it, but object oriented domain modeling really does feel more natural for certain classes of problem.

On the downside, F# lacks higher kinded types, and you're absolutely on your own when it comes to making sure things that should be pure are actually pure.