I actually started learning Scala: completed Odersky's Coursera class and developed a Play 2 project in Scala. Overall I like it, but reading others' code is often frustrating, shorthand shortcuts in language are still kinda alien looking, and even figuring how to handle simple things like multi-file upload with Play's controllers, I feel I don't quite understand what the hell is going on underneath all that magical functional code that I myself wrote by assembling bits and pieces from elsewhere.

And then I watch stuff like Paul Phillips presentations [http://www.youtube.com/watch?v=4jh94gowim0] and I just don't know whether continuing to invest my time in Scala is a wise decision long-term.

I'll probably try Clojure at some point, but for production-grade projects I will do Java for now. I feel the most frustrating thing about tech is having to place bets constantly on what to invest your time learning. It's eerily similar to investing in stocks. You never know what's going to live or die. And I'm saying this as a former Delphi developer with multi-year experience. :)