Here's a good paper on using Haskell to write a commercial application. The authors are practical commercial programmers who tried Haskell to see if it was a more effective language than Ruby:
Experience Report: Haskell in the “Real World”
Writing a Commercial Application in a Lazy Functional Language
Of special interest is the "Problems and Disadvantages" section. It seems that space leaks which are a continuing source of trouble in the authors' application.
Reading this paper reminds me of Tenerife Skunkworks Haskell vs Erlang Reloaded. In that experiment a developer found that Erlang was much better than Haskell for real-time programming.