Although I agree that LightTable is a more polished clojure IDE, it doesn't do the one thing that ganarajpr mentioned: create lein projects for you through the UI.
Even though lein is easy to use, integration like this lowers the barrier to entry for new folks wanting to learn clojure, which is awesome.
You stole the words in my mouth.. I am going to cry plagiarism ;)
Doesn't anyone else find it odd that command-line tools would be a barrier to entry for programmers? Sure, I see it all the time; I just don't get what people are expecting.