Posting for my nickel knowledge as well as yours—assuming that you care about WordPress, of course: Explanation of WP User Levels [from WordPress Wiki].

Principle: each user can edit/modify posts and options for other users whose level is lesser than his own. The main differences occurr between levels 0 to 5; 6 to 10 have the same privileges but the difference is rank, i.e. a 8 could edit a 6 but not vice versa.

Expected Reference to User Reg System

I would suggest that the WP user registration system, in order to provide some user registration functionality beyond the posting of entries, be revised. If a 6-10 gradation of administrators is necessary, so be it; I am not sure that it is necessary.

I would probably argue for a few new classes of users:

1. -1: Users you want banned from your site. Their posts/comments remain in the db, but they are not presented by the db queries when building a page. This is equivalent to Slashcode’s -1 system.
2. 1: User can comment, but if comment moderation is set, their comments are not presented until moderated.
3. 2: User can comment, and their comments are presented regardless of moderation setting.

These three values would be set by any administrator.

To incorporate this, an upgrade script would have to create levels -1, 11, and 12, shift all users whose rank is greater than 1 up by two levels, and carry forward. Also, all code that level checks would have to be shifted accordingly.

I’d also suggest that the number system be supplemented by a taxonomy [Banned User, Registered User, Trusted User, Author, Editor, Administrator].