I have used functional programming in industrial projects since 1998; starting with a stage lighting system, which is still in use. I wrote it while still a research assistant. While I have a strong attachment to Scheme - I was project editor for the R6RS standard - I also use Racket, OCaml, Scala, Clojure, Erlang, F#, Haskell, and Star in a wide variety of projects from social pedagogy to semiconductor fab control.
My work continually force me to question if I am still on the path to correct, effective, and maintainable software. Time and again, functional approaches won out, and failures hid in the imperative and OO parts of my projects. Consequently, the journey from academic research to industrial applications also ironically marks a journey away from imperative objects towards functional purity. (Static types, not so much, however.) The talk is a tour through my industrial projects, I encourage you mine them for insights on how to write and not to write software.
I am CTO of Active Group.
We do most of our software development using functional programming.