The users should be listed as 6M\username (I'm making an assumption that's what you're seeing). This was implemented by design with the original provider (long before I became involved in the project). I can only guess at the reasons though on automatic login that's how the username is passed from the AD. I've written code to strip the domain from the username but never implemented it for a couple of reasons. The first is that I haven't found an elegant way to strip the domain name from existing usernames in the database or add it back in if the admin needed to and, second, how to handle things in a mixed-mode site (sites that use both the standard login and the AD provider). The real culprit is the specter of mix-mode sites as the potential for username conflicts exist. Example: Say that the dotnetnuke.com leadership decided to implement the AD provider for their employees on this site at this time and then hire some guys named Mike Hamiltion and his domain username is mikeh. Without the domain name preceding his username there would end up being a confilct of some sort (pretty sure my account would get the short end of the deal). Or, conversely, if the ability was there to strip the domain out of the username and when they implemented the AD provider they set it up that way and then realized there was a conflict between the two mikeh accounts so they wanted to put the domain in front of their employee accounts. I don't know the number of the registered users on the site but I believe it's > 500000. How do you tell what accounts are domain accounts and what accounts are external accounts.

When you look at the user accounts in the search box you can set the field it looks for. On the site I run for the school I work for I usually just do a search on the person's first name.