You'll have lots of fun picking up Clojure. I'd recommend 'Clojure programming' by Chas Emerick... or 'Programming Clojure' by Stuart Halloway.. to get started and then 'The Joy of Clojure' by Fogus. My advice would be to not immediately get bogged down by taking on a large project (like an existing rails app) if you don't already have some experience with functional programming. You'll have a much nicer perspective on the Clojure way of doing things after you work through those books.