We're using it happily at Yieldbot. We're an ad network, and the core matching technology (which finds relevant ads based on the contents of the page and decides which one to show and how much to bid) is all Clojure. All the data science stuff is Clojure (it's been great with Spark and pretty good with Storm). The data pipeline is all Clojure now. The central database for ad campaigns and such is Datomic. The APIs for the frontends are moving to Clojure.

ClojureScript never caught on for the front-end work. There are some substantial services for which Elixir was chosen instead of Clojure.