If an administrator account switches to Gmail’s new look, the ‘Manage this domain’ link moves from its current location, to the Settings gear menu in the upper right of the Gmail inbox.
Blogs posts http://googleappsupdates.blogspot.com/2011/10/temporary-relocation-of-manage-this.html
http://googleappsupdates.blogspot.com/2011/11/manage-this-domain-link-for.html