I play with ldap servers and use Net::LDAP, it is fairly simple to use and has sound documentation. There is a Mozilla::LDAP module that you can use, I stay away from it due to the fact that you need to Netscape SDK to make it run.
An ldap directory is very efficient for large amounts of relatively static information. It is optimized for frequent reads, and infrequent writes. Typically it is used for information such as enterprise/academic directories, where the information does not change all that frequently.
in reply to LDAP and MySQL modules
"The social dynamics of the net are a direct consequence of the fact that nobody has yet developed a Remote Strangulation Protocol." -- Larry