DistributedMetadata. Instead of having a centrally defined set of metadata, distributed metadata tries to let everyone organise the world as they see fit. The challenge is: how to tie these different ways of organising the world together again?  [IAwiki]

Not much else over there yet, but the question is a fundamental one. An important problem is how to make people want to tie these ways together. For this I think we have to tap into people's innate propensity for sociality and curiosity towards new people with a common interest. The idea is to consider categories as rallying points. See ridiculously easy group-forming and BlogChannels for loosely joining webloggers. And if you're a diehard, join the fun at our group-forming community. (Will I ever stop those shameless plugs?)