According to many sources I shouldn't have to do anything special to get add users from a "internal" two-way trusted domain into SharePoint. And I can add them to the CA web app but not the "multi-tenant" host named site collections. I followed the articles on harbar.net to setup the multi-tenant environment and everything else works great.
Each tenant is assigned a specific OU in Active Directory, is that what is causing all the grief? How would I go about authenticating trusted domain users in a multi-tenant setup???