I had missed this in Charles Oliver Nutter’s original post:
So what happened? Sometime around JavaOne we heard about the Ruby KaiGi in Japan, a Ruby conference or get-together of some sort. If RubyConf is the big conference for us Westerners, this at least provided a mid-year update for English-speaking Rubyists. Matz was there, Koichi was there, and I believe other Ruby dignitaries made the trip as well.
And then Matz and Koichi dropped the bomb: Ruby 2.0 would support neither continuations nor green threads.
Don Box and James Robertson both linked to it today. While I don’t see much loss in dropping green threads, I’m not so sure about continuations … apart from continuation-based Web frameworks, I really like examples such as Sam Ruby’s Expat-based pull parser.