Starbucks uses a system with a Haskell frontend and backend for generating their personalized offers. I have it on good authority that it's probably been responsible for more than a billion dollars in revenue lift for Starbucks.
I have heard of Haskell used in companies mentioned by other comments, but I am surprised, pleasantly, that Starbucks uses Haskell.
Do you have a pointer (job posting, blog post, etc.) to Starbucks using Haskell? It could help me push for using Haskell by my employer, for example.