Finally Samba has released a preview of the next generation of their software. It has many interesting stuff starting from Active Directory-like working environment with its own small LDAP and Kerberos server included. Integrated SWAT (web-based administration interface to Samba) and many more. Even a one-click migration from Windows 2003 AD-based PDC to samba with all the machines/users and other stuff.
I am waiting for the stable release a lot, since I really like this topic and spend a lot of time around it. So far I have a couple of places where Samba (3) is acting as PDC for Win XP clients and I am happy, but there are some limitations and uncomfortabilities which I hope will be solved in the 4th branch of Samba.