I know theirs a plugin which provides added and custom roles, but it is buggy, development is at a halt, and it would be nicer if it were implemented by default.
- Provide an added Permissions Role where the user can only update pages assigned to their user name
- assign upload quotas for separate users
- Have administrators approve/deny new/edited posts/pages
- Make the permissions more flexible (for instance, now, if you enable edit_pages, it provides access to also ADDING new pages, rather than only edit existing pages)
- System could also benefit if it factored other restraints (like above edit_pages would allow the editing of any pages on the blog, where something more appropriate like edit_own_pages or edit_published_pages would restrict which pages the user could edit.)
- The Roles could be edited to the users liking, (like the Role Manager Plugin) and should also be able to restrict/grant access to the different pages in the Admin Panel as well as set the different criteria in what users can do on those pages (Ie. Allowing them access to Manage -> Pages would show the tab in the navigation and provide access to editing all of the pages; by selecting edit_own_pages would allow them to edit ONLY their pages.)
It can be as simple or as complicated as you want it to be :)