A group of economists at Ebay ran a series of experiments to measure the value or promoted links when the brand already own the top organic link http://faculty.

A group of economists at Ebay ran a series of experiments to measure the value or promoted links when the brand already own the top organic link http://faculty.haas.berkeley.edu/stadelis/Tadelis.pdf http://faculty.haas.berkeley.edu/stadelis/Tadelis.pdf They find no measurable short term benefit to purchasing the "Ebay" keyword on sales.