Found this great article today written by the Configuration Manager Support Team.

When building a Windows Vista or newer reference image (Windows 7, Windows Server 2008, Windows Server 2008 R2), to create a custom Default User profile based on modifications done on the local Administrator profile normally the CopyProfile option is used in an Unattend.xml file. However, since System Center Configuration Manager 2007 creates its own Unattend.xml file the CopyProfile option cannot be specified

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