Michael Hartl announces the Rails Tutorial Vanguard(railstutorial.org)

  # ActiveRecord query syntax
  2.X: User.all(:conditions => {:name => "aaron"}, :limit => 1)
  3.X: User.where(:name => "aaron").limit(1)
  
  # ActionMailer API now closely matches the ActionController API
  2.X: 
    class Notifier
      def user_notification(user)
        recipients  user.email
        subject     "test subject"
        from        "[email protected]"
        body        :user => user
      end
    end
    
  3.X:
    class Notifier
      default :from => "[email protected]"
      
      def user_notification(user)
        @user = user
      end
    end