Clojure keyword arguments

To update this answer for Clojure 1.2 there is now full keyword arg support with defaults provided by the map forms of destructuring binding:

user> (defn foo [bar &{ :keys [baz quux] 
                        :or {baz "baz_default" quux "quux_default"}}]
         (list bar baz quux))
#'user/foo

user> (foo 1 :quux 3)
(1 "baz_default" 3)