“Demystifying LDAP”

There’s a pretty good introductory article to LDAP in the sys-admin section of O’Reilly Network, entitled “Demystifying LDAP“.
The article introduces the concepts for LDAP and discuss the value of directory servers over databases: open standards for the protocol, open standards for the schema. And also the ease of use.
And if you still consider that deploying a directory server is difficult, wait until Sun Directory Server 6 is released and give it a try.