Joomla 1.6 already demonstrates the ability to add your own user groups and access levels. Recently the groundwork for the new permissions system was completed and is ready to showcase.
Understanding the Structure of Joomla is an invaluable reference PDF for all web site masters wanting to set up a Joomla web site. Download the PDF: understanding_the_structure_of_joomla.pdf Diagrams explaining the structure of the Joomla...
Ever wondered how Joomla sections and categories and the frontpage all fit together? Or maybe how the menus modules are arranged, or how to get around the 2-category limit? I see these questions a lot so I've put together a PDF of diagrams...