I'm more concerned about legibility of Scala code. I've been using Scala in anger for about two years now and I still find myself writing what seems to me to be idiomatic Scala code that I have a lot of trouble reading three days later. (Play makes this worse, I find, because of the way that objects are exposed into your scope--these objects are super handy, but tracking down where they're coming from and what they're doing produces nontrivial cognitive load.)