Getting OT: At a former place of employment, I used LDAP as a sort of modern-day NIS. PAM allowed us to use the LDAP for authentication and NSS caused users/groups to be looked up in the LDAP (if they couldn't be found in the files). Our Samba server was plugged into the LDAP in such a way, and that alleviated us from having to do anything special to manage permissions. We simply set the typical user and group permissions the way we would have if the users were local, and it worked like a charm.
Perl was involved, of course. Since we never found anything that allowed us to manage users and groups in a pleasant way, I used Net::LDAP and Gtk2 to put something together that I could hand off to the IT staff and not worry about. Last I heard, they were still using it to good effect.
Trying to bring this back on-topic, as cutlass2006 writes, LDAP can be an excellent solution to multi-faceted authentication. The only warning I can give is that you may be rolling-your-own on a lot of things, as we had to. Those are the two sides of the same coin: LDAP is extremely flexible, and as such you have to bend it to do your bidding.