Post Panda, it would seem that Google might be encouraging negative SEO campaigns.
This is an interesting discussion about Negative SEO involving Dan Thies
- a recognised WhiteHat in the industry.
To summarise, he claims that two of his websites have received "unnatural link" messages in Google's webmaster tools
(this is the method Google is employing to inform website owners that they have unnnatural links) despite his sites never having undergoing any link building campaigns.
So, in his eyes, someone has purposely built spammy links to his website.
I've always said, it doesn't matter what links you have to your site, Google would devalue a link before it devalues the site IN the link. But it seems they are no longer holding to that maxim.
So the question now is, are they actively encouraging people to go out and spam links to their competition to kill them off?
It would seem to me that Google is creating a counter-productive situation that would actually create multitudes more spam in the index. Not reduce it.