I really like your presentation. It´s a really cool combination of asynchronous performance increase and keeping code logic readable.
Did you hear about similar projects in JRuby?
Fibers are mapped to threads in JRuby so I doubt doing the same would be such a good solution, regarding memory usage.

Great presentation, I learned a lot from it. I wrote up an intro to fibers on my blog that others might find useful when trying to wrap their heads around of the flow of execution gets transferred from one part of the program to another.

http://paulbarry.com/articles/2010/04/01/fibers-in-ruby-1-9