send should never be used in a function that will not keep the CPU busy, such as one that calls Thread/sleep. send-off, which will allocate a new thread rather than taking up a slot in Clojure's fixed-size agent thread pool, should be used instead.
Another great tool in the Programmer tool kit. If you wanted this same concept on Scala or Java I recommend Akka2<p><a href="http://doc.akka.io/docs/akka/2.0.2/scala/agents.html" rel="nofollow">http://doc.akka.io/docs/akka/2.0.2/scala/agents.html</a>