As described by Charles Nutter, each lambda in Clojure is an anonymous class in Java. The problem is that classes are never garbage collected. They reside in a special place called the PermGen."

I know very little about Clojure, but that seems like a huge problem for Clojure, and other functional-ish JVM languages. Is it?

I've used Rhino (JavaScript on JVM) extensively, and I don't think it suffers from this.