Eric White has written an interesting post titled "Are developers using LINQ?" - there are interesting considerations about the adoption of functional programming too, but the most interesting part for me is the list of comment of the post. A lot of people described the adoption of LINQ into their team or company, and there is a spread variety of comments (good and bad).
An interesting comment is about the future adoption of F# when it will be shipped, because of the complete adoption of functional programming (C# 3 is not a complete functional programming like F# is). I suggest you to take a look at this post and its comments, because it gives you an idea of what is going on out there.