Here's the slides from “JRuby: Enterprise 2.0″ from our recent talks at Sun Tech Day and the ACS Web Technologies SIG.
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* The lack of C extensions in JRuby isn't a disadvantage in some opinions 😉 Plus you could have them if you really really really wanted to
* Rails doesn't have an O/RM. ActiveRecord is Active Record. There's no mapping, you pollute your domain directly from the database schema 🙂