Haskell is used for critical projects in production at Standard Chartered, Barclays and Facebook. There are also numerous startups. For both parallelism and concurrency, Haskell has a particularly good story. There's now even an O'Reilly book: "Parallel and Concurrent Programming in Haskell"

http://chimera.labs.oreilly.com/books/1230000000929/index.ht...