Also, just as a counterpoint to all this - as PG pointed out in his book, with Moore's law, speed of execution is no longer the limiting factor in most software development. It is programmer time and productivity, where (I'm guessing) Rails still wins this test. I'd expect that to be an ongoing trend. But of course speed of execution is still necessary in special situations, so this is still valuable.
I think Play+Scala should be competitive with Rails in expressiveness, while still being a lot faster. Of course, if you prefer dynamic typing you might disagree with me here.
Personally, I've found it's very expressive and easy to follow, although I'm using Java play. And having reliable autocomplete and ctrl+click navigation is something I really missed in Rails, but have in Play.
And hadn't heard of Play! Will check into that.
Also, just as a counterpoint to all this - as PG pointed out in his book, with Moore's law, speed of execution is no longer the limiting factor in most software development. It is programmer time and productivity, where (I'm guessing) Rails still wins this test. I'd expect that to be an ongoing trend. But of course speed of execution is still necessary in special situations, so this is still valuable.