One of the writers on my site (mediahug.com) pointed this out to me:
http://www.mediahug.com/almax/2006/07/01/a-coke-ad-worth-seeing/
He is worried because guests can successfully impersonate another user just by filling out the same name. He would like to know if the next wordpress update will allow admins to ban user impersonation. Is it possible to make it more clear that the user posting is a Guest, and not a user?