For the Amazon_store Drupal module I've been working on for Alonovo.com, I set up several of the pages to use Panels plugins. But there isn't a lot of documentation on how to do this, so I had to dive in and learn it from the examples available in the code. The result was a set of examples of how an drupal module can implement panes, the Panels Plugin Example which is now available on on Drupal.org.  There are examples of content_type, argument, context, and relationship plugins.  I'm hoping that others will review the code and improve it.