Comment 7 for bug 616719

Klaus: in an environment of this size, I strongly recommend against using libnss-ldap, because it just doesn't scale well enough. Please try installing nslcd and libnss-ldapd (notice the d), get it running, after that add nscd again, and evaluate if this better fits your needs. If it doesn't, you might also have a look at sssd and libnss-sss, but AFAICR that's only really available starting from maverick.
BTW both these daemons come with their own pam packages, which replace libpam-ldap.