gistfile1.clj

(defn throttle-chan [input]
  (let [throttle-chan (chan)
        output-chan (chan)]
    (go
     (loop [throttle-msec nil]
       (let [t-chan (when-not (= :disabled throttle-msec)
                         (timeout throttle-msec))
             [val c] (alt! [input throttle-chan])]
         (if (= c throttle-chan)
           (recur val)
           (do
             (>! output-chan val)
             (when t-chan
               (<! t-chan))
             (recur throttle-msec))))))
    [output-chan throttle-chan]))

A way to toggle

(defn toggled-fan-out [source]
  (let [a (chan)
         b (chan)
         t (chan)]
    (go
      (loop [ts (cycle [a b])]
         (let [current (first ts)
                [v c] (alts! [t source])]
            (if (= c t) ;; got a toggle message
               (recur (rest ts))
               (do
                 (>! current v)
                 (recur ts)))))
    {:a a
     :b b
     :toggle t})))