Jozef Imrich who wrote a wonderful, gripping true story of his escape from Communist held Czechoslovakia called Cold River just left a Comment on my recent why Amazon Should Blog post made mention of the pain that bad reviews on Amazon cause. That gave me an idea.
Amazon could allow authors to respond to reviews. That would create a person dialog and be fascinating to follow. It also might do something Amazon's Connect, it's author blog does not yet do--it could join the overall conversation of the blogosphere.
Sorry, I can't tell you how that would impact ROI, but I bet it would be more positive than negative.