To add to the evidence, I'm an experienced Python programmer who is currently waiting very impatiently for his Amazon shipment of "Real World Haskell" and "Purely Functional Data Structures". (Oh, and "Garfield Minus Garfield".)
http://book.realworldhaskell.org/
http://programming-scala.labs.oreilly.com/
http://caml.inria.fr/pub/docs/oreilly-book/
http://www.freetechbooks.com/introduction-to-objective-caml-...
don't know of any freely available content books on Clojure or Erlang;