I don't agree, I'd advise not to try Leiningen until you're comfortable enough with the parenthesis, the REPL and finish the koans themselves. This is 'getting your feet wet on Clojure', koans style. No need to introduce yet another tool when you're not dealing with the issues which Leinengen solves: managing library dependencies and configuration.
I remember I did: the koans first, then tried several exercises on the 4clojure website, then learned about Leinengen and only then I moved into 'projects'.
Ok, but the site's first suggestion is to use Leiningen to install the koans. It links to a generic Leiningen installation page, but then doesn't tell you how to use it to install the koans.
Unless they expect the new user to spend significant time learning about that tool before moving on to their koans, I think it'd really be much better to have a short how-to for that.
Learn Leiningen- not only because it makes Clojure simple and pleasurable to use, but because it'd be a fantastic tool no matter what language it was part of.
Project skeletons (new new), command line scripting (via lein exec), deployment, the wonderful 'lein ring server', custom plugins... and for those who just want to get their feet wet, 'lein repl' brings the ocean to you.
My initial reaction was to upvote @eccp, based on my experience with leiningen the first time round. Long story short: went around in circles following outdated (but seemingly comprehensive) guides that twisted my mind with hopeless combinations of Ant, Maven, Leiningen, emacs, slime and swank, among others. Basically gave up after a while, but was fortunate to get some encouragement here on HN, and went back in with just leiningen and emacs. I recall that was just the right mix, and as you say, lein repl pretty much brought the ocean to me.
If you have lein, you can run `lein repl` which provides awesome tab-completions, documentation, and source for any given function. Pretty handy for beginners I'd say!
I remember I did: the koans first, then tried several exercises on the 4clojure website, then learned about Leinengen and only then I moved into 'projects'.