The only downers I care about are stack traces in "Java" rather than Clojure and the lack of TCO in the JVM.
I think there's some work going on to address the former. The latter issue isn't really that bad unless you need to use trampoline, which I don't care for because it means the functions have to be written to know they'll be used in this way.
Regardless, Clojure is one of my favorite languages.