[huahaiy]

I think the ratio of people using functional language that work on "hard" problems should be a lot higher than the mainstream language users.

From my personal experience, before I become a Clojure user, I wouldn't dare to write "hard" software such as compiler, database, and such, all by myself. Now I have done all that, I would credit part of that to the productivity of the language. That's why with such a small community, Clojure ecosystem has produced so many first of its kind innovative systems, e.g. Storm, Datomic, etc.