Simon Peyton Jones had a talk with a very nice overview of concurrency in Haskell. He is a very good presenter as well :).

http://www.youtube.com/watch?v=hlyQjK1qjw8

There are a lot of concurrency related libraries implementing all kind of abstractions. Distributed computation is upcoming. There is an overview here: http://www.haskell.org/haskellwiki/Applications_and_librarie...

one big kick, since haskell is pure functional you don't have state (okay, in terms that imperative programmer use that term) and all data are immutable.