You should read The Moral Animal by Robert Wright, I’ve been enjoying it immensely.
Spreading the word that someone has cheated you is potent retaliation, since it leads people to withhold altruism from that person for fear of getting burned. This may help explain the evolution of the “grievance”–not just the sense of having been wronged, but the urge to publicly articulate it. People spend lots of time sharing grievances, listening to grievances, deciding whether the grievances are just, and amending their attitudes toward the accused accordingly. (pgs 207-208)
Half of blog posts seem to be publicly articulating grievances. And not only about people; products, companies, websites, policies, whatever.
The problem is that this method relies on human memory to remember the grievance and lower the reputation of the item or person in question. Now that the whole world is fair game (rather than just your village or tribe), the human brain just isn’t up to the task of keeping track of so many reputations. The web is already becoming a bit of a collective memory of these things, but it needs to be organized better. Google’s PageRank just isn’t cutting it. I want something better, I’m building something better.