gistfile1.clj

(time
 (let [*pdfs-proms* (map (fn [[pdf id]] [pdf id (promise)]) *pdfs*)]

   (doseq [[pdf id prom] *pdfs-proms*]
     (future
      (do
        (spit (str id ".pdf") (slurp (java.net.URL. pdf)))
        (deliver prom :ok))))

   (doseq [[_ _ prom] *pdfs-proms*]
     (deref prom))))
;; Elapsed time: 346.363 msecs