I'm unlikely to give it a serious try because I find the complexity of the Scala language to be pretty scary. Still, I'm curious: how fast is the compiler? Does it generate compact code? Clear error messages?
I haven't tried scala.js yet, but I've gone through some presentation slides...they're claiming compact code that runs as fast as javascript, clear error messages that point to the line of scala sourcecode, and even some advantages over jvm scala (though I forget the details). Don't know about compile speed.