Taxonomy Limit Module
If your Drupal site has multiple content creators, this module allows your site administrators to enforce good house keeping practices by limiting the number of terms that a node can have per vocabulary. This limit setting can be specified per content type as well as per page (node).
The settings page for this module provides added information to help you choose optimal settings. Also, this modules comes with redundant checks for the categories you select so that changes to how the category is configured won't cause errors in other areas of you site. This module allows for some customizability such as the stock error messages (that appear if a user chooses too many terms) can be customized independently for each category and/or each content type.
