Using the presented configuration options to enable Active Directory authentication generates a significant number of "winbindd[#####]: ads_find_dc: failed to find a valid DC on our site (Default-First-Site-Name), trying to find another DC" errors. This occurred using Freenas 0.7.2 Sabanda, including the most recent rev 5543.
The fix for this is to add the "password server = your.kerberos.server" option to smb.conf. This should be a option available from the configuration screen instead of having to add it to the Auxiliary Parameters section.
I found the fix in the official samba documentation here: http://www.samba.org/samba/docs/man/Samba-HOWTO-Collection/domain-member.html#ads-member
