I have Samba 3.0.14a (Debian's build 3.0.14a-3) working as a Windows 2003 SP1/2000 network. Since SP1 I'm getting a lot of errors and smbclient does not work when using kerberos auth (sometimes, surprisingly, it does work). I'm also getting some "unknown auth type 9" messages in Samba logs when I'm trying to access shares from windows machines. "getent passwd" is working fine, Squid is authenticating AD users normally through winbind, but Samba is completely borked.
This should be cleaned up in 3.0.21. The code is already in trunk.