I got somewhere between 2.0 and 2.2 "milliseconds per ping" for Scala 2.9, and somewhere between 3.5 and 3.7 for Go 1.1. This is not the 10x difference that the authors reported, but it is something. The difference may be due in part to the different platform and hardware I am using.
Contrary to what I wrote earlier, I noticed that GOMAXPROCS=8 did seem to be slower than GOMAXPROCS=4 here. I got around 4 "milliseconds per ping" with GOMAXPROCS=8. Using a mutex and explicit condition variable shaved off maybe 0.2 milliseconds on average (very rough estimation).
Again contrary to what I wrote earlier, Nagle on versus off didn't seem to matter in the Go code. I still think you should always have it off for a test like this, but on my setup I did not see a difference.
I still don't think this benchmark is showing what they think it is. I have a hunch that this is more of a scheduler benchmark than a TCP benchmark at all. I think I'd have to haul out vtune to get any further, and I'm getting kind of tired (after midnight here).