Drupal's filter system is a pretty nifty thing- you can grab text coming through the system and modify it to your hearts content. This makes for great things like replacing various kinds of tokens, automatically making URLs link, and so on. I've been looking at the wordfilter module to check for "bad words" coming through the text.
One of the things that this module lacks is logging of the users who are using "bad words". Being able to track usage by user creates the possibility of creating specific kinds of actions around the user- settings various flags, demoting permissions, alerting admin, etc.