I have been playing around with the cvs version of drupal to set up a web site that I will ultimately want to be for members of my family. As such, most content will be restricted to the family, with a deliberate decision on behalf of a poster to make it publically available (essentially to the anonymous user).
I have downloaded what I presume is some trial version of a nodeperm_role.mode from JonBob's Sandbox and installed it into my installation.
The most immediate effect is that when editing a node, you get a list of roles, to select who may view and who may edit the node. However, despite creating a bit of content and testing what happened - I always got to see the content, even as an anonymous user.
I bit of poking around to understand how accesses are permitted or not uncovered whats happening.
The "node_access" table is being scanned for user records that contain either a node id of 0 or the node currently being checked to see if the user role should see it. Within that, the user has a number of access rights, which with the nodeperm_role installed include 'rolen rights when n is the number of the user role id. The anonymous user is role1 and authenticated user is role2. If other roles are added they will have similar grant privilages. It seems that the access system also gives every user the 'all0' privilage.