How much does Google know about the sites you own? And can that be used to your advantage, or to hurt you?
Over the past decade Google has spent an incredible amount of energy trying to figure out administrative relationships between websites, both to help you and sometimes to discount links between those sites with potentially negative consequences.
http://moz.com/blog/how-google-knows-what-sites-you-control-and-why-it-matters-whiteboard-friday
Social tagging: Google > links > ownership
