Post hoc filtering
In a world where publishing is expensive, the act of publishing is also a statement of quality -- the filter comes before the publication. In a world where publishing is cheap, putting something out there says nothing about its quality. It's what happens after it gets published that matters. If people don't point to it, other people won't read it.
Clay Shirky, in a marvellous essay on ontologies, categorisation, links and tagging.