I have often come across elements of F# in my work and even strong arguments for converting C# code to F# – great article from one of the worlds big .NET players on the issue – take a look:

http://ayende.com/blog/170849/why-ravendb-isnt-written-in-f-or-the-cost-of-the-esoteric-choice

He nails it as far as I am concerned – very practical approach to the debate.