Customizing Default Users Profile Using CopyProfile In Unattend.xml
Here is a great post over on TechNet by Jeff Hugh on how to properly use the CopyProfile feature:
http://blogs.technet.com/b/askcore/archive/2010/07/19/customizing-default-users-profile-using-copyprofile.aspx
This is a great read and covers both ConfigMgr and MDT usage.