First Monday has an interesting article on collaborative reputation systems, aka trust metrics. I'm working in this field for the non-profit collaborative publishing project which I've written about before, called thingster.
But we suggest the potential utility of reputation services is far greater, touching nearly every aspect of society. By leveraging our limited and local human judgement power with collective networked filtering, it is possible to promote an interconnected ecology of socially beneficial reputation systems — to restrain the baser side of human nature, while unleashing positive social changes and enabling the realization of ever higher goals." [Manifesto for the Reputation Society]