[HillOBeans]

This. The immutable nature of Clojure is what, IMHO, makes it such a better choice than Java for me. I frequently see discussions/debates around type safety on HN, but in my experience, it has been the mutable nature of Java systems that has created more bugs than anything else. Clojure being immutable by default has drastically reduced the pain caused by these bugs. Clojure's collections, FP style, and meta-programming (via macros) all make it a great choice for me, but I think being immutable by default is the biggest thing.