Making Clojure easier for newcomers would be a boon - I've battled with setup and configuration each time I've tried to use Clojure. Having a simple but powerful REPL environment like IPython would be fantastic.
Download and install leiningen (http://leiningen.org) and then you can start up a repl with 'lein repl'.
I wrote a little web app using clojure and when it came to deployment I was really positively surprised:
1) 'lein ring uberwar'
2) copy resulting war file into your tomcat webapps directory
3) you're done
There's also a heroku plugin if you don't like hosting yourself.
Without leiningen clojure is just unusable though. You have to mess with classpathes and wrapping java command line calls in boilerplate.