To me, Jon Udell's post on Wikipedia and the social construction of knowledge points up some problems with the centralized construction of knowledge. Yes, Wikipedia is cool, but attempting to build one true centralized repository of knowledge makes that repository a more desirable target for those who would manipulate your understanding of the world. Better, I think, to pursue a more decentralized approach -- not one community of knowledge, but many communities of knowledge. After all, decentralization is the Internet way, no?