http://jekor.com/article/is-haskell-a-good-choice-for-web-applications

I was concerned that Haskell wouldn't be able to handle the task. I'd had experience working on large websites with Perl and PHP, and a part of me doubted that Haskell's no-compromises approach would work for anything serious and large-scale. At the time, "Real World Haskell" wasn't yet published, and I could find no examples of large Haskell web applications.4 Much of the libraries in Hackage seemed to be toys compared to what I was used to.

But now, having launched the site I can say: yes. Not only is Haskell capable, it's an excellent choice.