Our ldap setup for authentication, on our internal web servers, had been working fine under debian 3.1 (sarge) for some time when we upgraded to etch (4.0) Suddenly it stopped working.
mod-pam and ldap authentication
Originaly we made use of the mod_pam module as it was easier to setup pam to authenticate with ldap, than use the continually changing ldap plugins that existed for apache.