I think I can safely say it isn't used heavily in many production environments but it is used heavily in some. For example, one of Facebook's abuse systems, dealing with 1M requests per second is written in Haskell: https://code.facebook.com/posts/745068642270222/fighting-spa...
As for particular places where it shines, I don't know of any in particular. I remember when taking my Declarative Programming course in university my lecturer loved to talk about an experiment the military did where they challenged a few teams to implement some kind of radar system in their chosen language and evaluated them based on time taken, correctness and code complexity (LOC) at the end. The Haskell team performed very very well. I can't find any details on this experiment though...