I don't know, as far as I know functional programming is a standard course in computer science university curriculum. I've only been part of small dev teams so far, but of those teams always more than half were university educated, and none of them continued functional programming after university. Of all my university friends only one did Haskell outside of university that I know of (maybe there's some secret Scala/F# lovers at Java/.net firms). I've been part of the Haskell community, so it's not like I don't know Haskell programmers, but I'm saying I know a lot of formally educated programmers, and only very few of them took a liking to functional programming to an extent they'd do it professionally or even as a hobby.
I think there are quite a few closet "functional" programmers, who may not even consider themselves as such, doing their best to write mostly side-effect-free, declarative code within the confines of an OO or multi-paradigm language (in .NET land, functional-ish features like LINQ and pattern-matching bleeding into C# makes this easier). I also met more than one person trying to introduce F#/Scala in a pretty small .NET shop I used to work for.
