Very nice comments from the author of ☞ Programming Clojure, Stuart Halloway:
[…] both Clojure and Scala are huge improvements over the language you are using right now. But you won’t be effective in either one of them tomorrow: the learning curve is not 1, but 5-10 books.
In fact, based on Rich Hickey, creator of ☞ Clojure, you can learn clojure in ☞ 36 books.