When I use the unattend.xml to join the domain on one DC I get the following in the NTSetup.log file. I have edited the file for security reasons.
NetpDoDomainJoin
03/12/2012 14:55:47:510 NetpMachineValidToJoin: 'MACHINE NAME'
03/12/2012 14:55:47:510 OS Version: 6.1
03/12/2012 14:55:47:510 Build number: 7601 (7601.win7sp1_rtm.101119-1850)
03/12/2012 14:55:47:510 ServicePack: Service Pack 1
03/12/2012 14:55:47:510 SKU: Windows 7 Enterprise
03/12/2012 14:55:47:510 NetpDomainJoinLicensingCheck: ulLicenseValue=1, Status: 0x0
03/12/2012 14:55:47:510 NetpGetLsaPrimaryDomain: status: 0x0
03/12/2012 14:55:47:510 NetpMachineValidToJoin: status: 0x0
03/12/2012 14:55:47:510 NetpJoinDomain
03/12/2012 14:55:47:510 Machine: MACHINE NAME
03/12/2012 14:55:47:510 Domain: DOMAINNAME\SERVERNAME
03/12/2012 14:55:47:510 MachineAccountOU: (NULL)
03/12/2012 14:55:47:510 Account: DOMAINNAME\USER NAME
03/12/2012 14:55:47:510 Options: 0x23
03/12/2012 14:55:47:510 NetpLoadParameters: loading registry parameters...
03/12/2012 14:55:47:510 NetpLoadParameters: DNSNameResolutionRequired not found, defaulting to '1' 0x2
03/12/2012 14:55:47:510 NetpLoadParameters: DomainCompatibilityMode not found, defaulting to '0' 0x2
03/12/2012 14:55:47:510 NetpLoadParameters: status: 0x2
03/12/2012 14:55:47:510 NetpValidateName: checking to see if 'DOMAIN' is valid as type 3 name
03/12/2012 14:55:47:728 NetpCheckDomainNameIsValid [ Exists ] for 'DOMAIN' returned 0x0
03/12/2012 14:55:47:728 NetpValidateName: name 'DOMAIN' is valid for type 3
03/12/2012 14:55:47:728 NetUseAdd to \\SERVER\IPC$ returned 53
03/12/2012 14:55:47:728 NetpJoinDomain: status of connecting to dc '\\SERVER': 0x35
03/12/2012 14:55:47:728 NetpJoinDomainOnDs: Function exits with status of: 0x35
03/12/2012 14:55:47:728 NetpDoDomainJoin: status: 0x35