Tag was correct in In-Portal versions prior to 5.2.0, because Users.Username (former PortalUser.Login) field always was present and was filled with e-mail as fallback.
Now this field can be empty and we need to show user's e-mail instead. I've created <inp2:u_UserSelectorTitle/> tag for exactly same purpose and we can use it there. It has "Selector" in it's name, because it was created to be used inside user selector, where such problem also was present.
If there are any ideas how to properly name that tag, then I'm ready to hear them.