Say hello to fully automated GitHub mirrors of every plugin in the WordPress.org plugin repository. These aren't your typical plugin Git repositories. These mirrors can be used for fast, efficient, and automated plugin updates using Composer, and don't require "sync scripts" or separate Subversion checkouts for plugin development. They also offer a way for plugin developers to make the move to Git even while others continue working on the same plugin using Subversion uninterrupted.
Plugin Developer Guide - The black art of using Git with a SVN repository. Published in April 2013 by Bryan Petty
Add New Guide - How are you using the plugin mirror? Published in November 2013 by Bryan Petty