Groovy++ is working on improving the performance: http://code.google.com/p/groovypptest/
You kidding? Clojure is nice precisely because it's an un-Java as it can possibly be.
Exactly. If one want a Java-but-less-painful, Clojure ain't it.
I'd recommend Scala even if you skip all the functional parts of it (Clojure's too un-java to speak as an alternative.)