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GitHub User: damien
For JRuby, you can use JRuby's bundled Nailgun server as an alternative to Spork. It'll be very familiar if you've ever run RSpec with a DRB server: http://blog.headius.com/2009/05/jruby-nailgun-support-in-130.html
It really, really is. The only downsides I've seen are managing a lot of junk accounts from expired sessions and limiting DB load when migrating/deleting guest users.
Ryan covers a simple solution for guest deletion here, but if you were to implement something similar in production you'd probably want to limit it to guest accounts who's sessions had expired. This is definitely stuff you'd probably be best off running as a background process or worker.