Comment Use Univention UCS (Score 1) 452
Its a Debian based business Server with an ldap directory backend. It spans multiple servers and roles. It seamlessly integrates samba4, so windows hosts are also happy with it.
It comes with a UCC (Univention Coorporate Client) which you can install via network boot. (just a few clicks.) Its KDE Based, lean and makes a lot of sense. Of course you can also hookup ubuntu.
I have done large installations 2500+ Users as well as 15 users shops with it.