There's no question whether or not negative seo works. It does. I've had it happen to more than one of my sites and what they did is over optimize the anchors with blog comments, forum profiles and all the shit links they could find. Obviously negative seo will not work on whitelisted websites, or will take a lot of effort on strong sites, but these are the times we now live in. What good is it to invest time into a site that ranks well only to have some dickwad nuke it with spam links so that their site can rank higher? Google does not give a shit either. All Google cares about is converting more website owners into Adwords users. And with every website penalized for link spam, Google will have the red carpet rolled out to justify showing only paid ads on the first page of the serps somewhere in the not so distant future.