I tiptoed around this a bit, but I think F# is great. I have little experience with it, but I work with someone who has been using it pretty extensively for a bit and we've talked about it a number of times.
This, however, is where the environment/culture issue (that I also danced around) comes into play. In most .NET shops it would be extremely hard if not almost impossible to bring in another programming paradigm like functional, let alone mix it. This is perhaps a bit ironic considering most of the same places use javascript, but if they could write C# instead of javascript on the client side, I'm certain most would (in fact when ASP.NET first made this somewhat possible it was the norm until people got bitten by all the pitfalls).
This, however, is where the environment/culture issue (that I also danced around) comes into play. In most .NET shops it would be extremely hard if not almost impossible to bring in another programming paradigm like functional, let alone mix it. This is perhaps a bit ironic considering most of the same places use javascript, but if they could write C# instead of javascript on the client side, I'm certain most would (in fact when ASP.NET first made this somewhat possible it was the norm until people got bitten by all the pitfalls).