I brought this up as a request before.
Why not have a warning system that displays in a meter or 'rank' style images to show the severity of their warning status, shadowed 'none' images if no warning, 10%, 20% etc.
This can be displayed in the forum under the users name/avatar/rank.
Also have this in the Users part of the administration panel so that Administrators can keep track of their users that have been breaking the rules on the site.
Upon warning the user the administrator puts the reason as to why they were warned for following up upon the situation and a private message is also sent to the user outlining as to why they were warned.
Throw in a Black card=10 and link it all into an auto-suspension sytem.
Perhaps have a drop down list of reasons when a warning is applied, and associate a reason with each warning.
User to see his own personal status through My Account.
I currently help to run a football based site, built upon PHPnuke 7.1, and me and the webmaster are slowly but surely porting over to cpgnuke, converting everything over on our test site beforehand, checking and double-checking etc.
Currently in our forums, we use the yellow card mod, the mod's forum can be found here.
You can download from the announcement thread called, appropriately, MOD download & history.
Now, the webmaster says that our php skills (being not quite newbies but not quite experts) are not good enough to port this mod over, and it is a perfect base for what you were describing above.
Would be absolutely fantastic is someone could port this over.
Server specs (Server OS / Apache / MySQL / PHP / DragonflyCMS):
Linux/Apache 2.0.50/MySQL 4.0.18 /PHP 4.3.9/CPG 8.2b
Joined: Aug 01, 2004