2012: Design Center Online is no longer a part of US English Language AutoCAD
The CAD Manager Control Utility indicates that US English language users of AutoCAD 2012 can install Design Center Online for use with Design Center however, when you start AutoCAD 2012, the Design Center Online does not appear.
Design Center Online was removed from AutoCAD 2012 US English because it is obsolete and was replaced by Seek. Since the CAD Manager Control Utility cannot be customized for specific localizations, the Design Center Online option cannot be removed from this tool.
Design Center for US English language has a button to access Autodesk Seek, the online design sharing community that replaced Design Center Online in 2010.