Here's some screencasts on RubyCocoa:

RubyCocoa - Bindings + ActiveRecord∞ by Eloy Duran
GettingStarted, installing RubyCocoa from svn/source∞ by Eloy Duran
Simple demo of working with the Rucola generators∞ by Eloy Duran
Detailed demo on creating a Rucola/RubyCocoa app through BDD∞ by Eloy Duran

RubyCocoa - FlickerViewer.app∞ by Fujimoto Hisa
Mac OS X Software Development with Ruby Part I∞ by Fujimoto Hisa
Mac OS X Software Development with Ruby Part II∞ by Fujimoto Hisa

Your first few days on RubyCoca∞ (blog post here∞) by Erik Kastner