The idea of shrinking obnoxious people's postings sounds like such a good idea! I'm sure there are good reasons why it would be a massive pain to implement, but, hell, I've got an O'Reilly book! (a little knowledge is dangerous, and all of that..)
It seems like one could add a 'moderation' value to the user's profile. Normally it would be 0, but as they get down moderated the value gets reduced by the moderators to negative numbers. From there, one would have to add a bit of PHP code (I think) for each posting that calls up the moderation value and if that value is less than 0, modifies the font size based on the moderation value. (It would also override any user set font size value) From what I can tell, font size isn't set on each post by default, but it wouldn't be much extra in terms of database access or volume of HTML being served up.
Just me talkin' crazy...
