Looking through the last couple of Who is hiring threads, I've noticed most of the software stacks seem to revolve around a "web friendly" language such as Java, Python, or Ruby, a RDBMS, and extensive Javascript--with the occasional NoSQL or Scala mention to round out the pack.
Besides a couple of "big names" like Ericsson using Erlang and Jane Street heavily using OCaml, I haven't seen many places advertising their stack as being based on a functional programming language. Hence, I was wondering if FP is gaining ground in production environments, and if so, who is using it.
If by "production" you mean application domains of software that startups typically write, the more statically-typed functional languages (i.e. those based on Hindley-Milner) like OCaml, SML, and Haskell are seen less frequently because startups are constantly changing their designs and features, and those languages aren't well suited for what pg calls exploratory programming. However, as you pointed out, Jane Street appears to be highly successful with OCaml (although they don't report their earnings), and several well-known FOSS projects like darcs and xmonad are written in Haskell.
Edit: Also, Ruby and Python are probably as well suited to functional programming as Scala is, outside of Scala's parallelization models that we tend to associate with functional programming. And I've certainly seen production code written in Ruby and Python. :)