NeverBlock provides a way to use fibers and rails and…never block.
It is also possible to use a NeverBlock spin off [mysqlplus] to be used in a threaded rails project (thus allowing you to have non blocking IO in the threaded realm, i.e. allowing rails to be true multi-threaded, once that happens with rails 2.2).
setup an edge rails project  [or use rails 2.2]
copy https://github.com/methodmissing/mysqlplus_adapter/tree library to the vendor/plugins directory
change your database.yml entries say mysqlplus instead of mysql
add pool: 4 to the database.yml entries [from ]
within environment.rb add
config.threadsafe! # from 
edit rails.rb within the mongrel gem and comment out any time it uses synchronize [since it's not thread ready]
ex on my machine:
then script/server should work in a multi-threaded way. Test by creating an action that is ActiveRecord::Base.connection.execute(“select sleep(1)”) and run two simultaneously requests–they should both come back in 1s.
Now if only rails 2.2 can come out…