Well, when people say FP they mean different things. The Erlang/Clojure kind bears little resemblance to the Haskell/scalaz sort discussed in the article. Neither does most of the Scala code written at Twitter (which is mostly OO with a sprinkling of functional).
That's hardly true. Erlang's event loops are based on a very similar kind of state encapsulation as Haskell's state monad. Really Erlang is littered with explicit monadic patterns but lacks a good system for abstracting over those patterns so you just call them "OTP" instead of a monad.
