not that it's the same at all, but your great question made me think of negative political ads. I can't find any research that clearly shows how effective negative campaigning is, but apparently >70% of ads this election season were negative or attack ads (http://mediaproject.wesleyan.edu/2012/05/02/jump-in-negativi...). That feels like a lot and I can't imagine that the smart people working on these campaigns would spend so much here if it didn't work as well as other tactics. I'd love to see metrics here too.