Yehuda Katz, member of the Rails core team, describes the many new ways to extend Rails 3, including the overall philosophy of extending ActionController and how to use ActiveModel to better integrate your non-ActiveRecord Ruby objects and Rails.
Author Mislav Marohnic discusses Coral, a way to pull in and organize Git repositories that extends and partially replaces RubyGems. Although still in the early stages, Coral aims to brings sanity to maintaining your own third-party forks across projects.
Lew Cirne, CEO of New Relic, outlines how they use their own RPM product to maintain and improve the performance of their application, which processes billions of transactions per month with the average response time under 40ms.