It was added recently.

There is a lot of activity in the language development leading to what I expect to be an exciting Clojure 1.1

[Edit] A link to the language definition: http://clojure.org/special_forms#toc10

Another link to a small but useful (for me, anyway) discussion: http://blog.fogus.me/2009/12/21/clojures-pre-and-post/

Just to reiterate, yes it was added in 1.1. I did not even know about it until 1.1 hit personally, so I dunno how many knew since I try to actively follow new feature additions. But maybe I'm just blind ;)