David Spector's articles hit a number of good points. Some of the comments about eDirectory, Novell, and AD technical details notwithstanding, I feel that his main points are completely valid. There is no standard, out-of-the box Open Source "domain controller." Everyone who wants a network-based authentication and directory service for their Linux/*BSD machines has to "roll their own" custom system....a royal pain in the behind that will prevent enterprises from adopting Open Source.
I am in the midst of a Kerb5/OpenLDAP rollout. What a pain! There is NO reason that Red Hat, SuSE, Debian, Mandrake, and others could not have a ready-to-go LDAP/Kerb5 solution right out of the box, with CLI and GUI admin tools. If they did, it would be THAT much easier to migrate away from Microsoft.
A good, interoperable, secure, Open Source directory/authentication system for Linux is not just a "missing piece", its a gaping hole!
"Roll your own" and eDirectory may work in some environments, but it won't capture the medium and small enterprises.