I build a lot of stuff with Incanter[1], clj-ml[2] and Quil[3] for building visualisations. None of this is as joined up or as thorough as the equivalent R (or probably Python) bits. Clojure open source libraries are also incredibly prone to being abandoned. Wouldn't trade the language in for anything though, and I've never seen any R code that I would want to maintain myself.

[1]: http://incanter.org/

[2]: https://github.com/joshuaeckroth/clj-ml

[3]: http://quil.info/

I personally use this in place of R, where possible: https://github.com/incanter/incanter

It has a very small portion of the mindshare. Almost everyone uses R, Python, or one of the proprietary things.

I use Clojure for any data science type tasks I have, but that is because I am primarily a Clojure developer.

It is very nice for a lot of basic data analytics -- but I doubt many full time data scientists use Clojure as their primary tool. The number of libraries available for R and Python is pretty amazing.