I think this is two, or maybe even three, different mods....
1. Private moderation - Where the admin can put some users under moderation, so that every post from that user needs to be approved by admins/mods before they are shown on the board. Maybe, it should also be possible to mark the post as muted, so the user can see it, but not anyone else, but it might not be needed if there already is a user muting function.
2. User muting - Admins can mute all new posts from a user, the user himself sees his own posts, but no-one else does (except admins/mods, who sees them with something like **MUTED** added to the subject and/or body).
3. Bozo Filter - Users can ignore certain users so that they won't see what they write. The content of all such posts are exchanged with the text "YOU HAVE MUTED THIS POST" and the subject is changed to "This post is muted" (or maybe with **MUTED**) added to it (we don't won't them to be intrusive though, they should be as unnoticable as is possible).
Combing these three functions should allow for a system with which you can keep a clean board without too much hassle.
