One of the problems that developers have to learn to address is concurrency. I expect this to be a recurring theme on this blog. From what I have seen Clojure is the language best suited to dealing with concurrency.
Rather than talking about the different problems of multi-threaded programming and how they are addressed with Clojure, as if it is some necessary evil, here is a great presentation about Clojure's strengths before even considering the issue of concurrency.
This is from Stuart Halloway, author of Programming Clojure. This was filmed at Øredev 2009.
It appears Vimeo doesn't want me to embed it, so here is the link:
Clojure - Stuart Halloway