You may enjoy to read about the architecture  behind the highly successful LinkedIn services used by millions of people. Dionysios G. Synodinos at InfoQ has been talking  to the technical people behind it all, Alejandro Crosa, Chris Conrad and Jay Kreps. They describe the architectural decisions, trade-offs and the benefits of bringing Scala into the equation and how it all plays together with JRuby and back-end databases. Alejandro is clear about Scala, "If you use Scala just like you would use Java then you are just getting a more succinct syntax and nothing else. Embrace immutability, functional data structures, pattern matching, Actors, etc. and you'll never go back."