Last week we successfully implemented Drupal as an Enterprise Portal for one of the largest IT Organization (Saudi Business Machine - SBM) in Saudi Arabia. Portal is very much optimised to support 50,000+ user base, portal has been developed over the course of six months with handful of resources.
Content moderation is based on a very powerfull module called ETools which has been developed inhouse, this module provides group based moderation and node access is based on the group of audience selected during the time of content creation. Etools implements an idea of group based content publishing called Publishing Entity. So every thing is treated as groups. Taxonomy terms created can automatically creates similar groups either (Publishing Entity, Private/Public Audience) if the taxonomy is Etools enabled, user tagged with such terms automatically become member of similar groups. In short its a very smart module that integrates very well with node access and workflow modules, Etools can also be configured to integrate with external systems like LDAP and SAP. Soon we are going to launch it on drupal.org for community collaboration.