You can be productive in clojure, I think, without being extremely fluent. But Clojure does tend to some perl-esque terseness. Browsing down this page (http://clojure.org/reader) everything is fine until you start getting into macro characters, and then the dispatch macro, and then the regex dispatch macro. I think you could write perfectly fine clojure code without knowing the details of all of these, but it can be frustrating to not know if your code is idiomatic clojure or merely badly translated from another language.