that's just semantics... set up the promotion so that if a user does not meet whatever goal you want, they get moved to another usergroup (non-mod). you can adjust the "promotion" accordingly.
GearTripper--You can't do this with the current promotion system, unless I'm missing something. The current promotions system only takes TOTAL posts into account. There's no way to set up a promotion based on posts per week/month/etc.
I would REALLY like to see this ability in a mod of some sort!