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.
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.
William Pietri and Amanda Willoughby revisit their Agile2008 talk "Meshing Gears: Real-world examples of how design and development integrate - and fail to"