I presented on August 30, 2010 to the DC WordPress group on the topic of the Users / Roles / Capabilities system in WordPress. I presented a small number of slides, and wrote four simple plugins to demonstrate some specific features. My slides (In HTML / CSS / JS, not some proprietary format) are available at http://aaron.jorb.in/slides/dcwp0810/. You can navigate through them with your arrow keys, or you press esc and it will take you to thumbnails where you can jump around.
I’ve also posted each of the plugins I wrote, along with a detailed explanation of them.
Shortcodes for Discrimination – Provides shortcodes that allow either users or non users to see certain content
Personalize Read More – Changes the Read More link to call out logged in users by name
Add Role – This adds a role for managing links and removes editors ability to
Repository containing all the code: http://code.google.com/p/wp-user-plugins/