As a result of the EU case, the Samba team gained access to Microsoft's documentation of the protocols it uses. This program is known as WSPP.
In March 2008, this documentation was made public, and is now available at http://msdn.microsoft.com/en-us/library/cc197979.aspx
Samba Team Documents
Andrew Bartlett's thesis on Samba4 and AD .
Stefan (metze) Metzmacher's thesis, covering the internal Samba architecture as it surrounds AD replication in particular.
Mailing list discussions
An extensive discussion on kerberos and Samba4 looking at how and why Samba4 uses it's own KDC, and why we can't just be 'normal'.
These are listed so that hopefully, in future the next rounds of such discussions don't have to go over the same ground.
Source code tools
The Samba Build farm tests Samba across a number of platforms, and provides code coverage statistics on our test-suite (now obsolete).