The Web has acquired immense value as an active, evolving repository of knowledge. It is now entering a new era, which has been called "Web 2.0". One of the essential elements of Web 2.0 is harnessing the collective intelligence of Web users. Large groups of people are remarkably intelligent, and are often smarter than the smartest people in them. Knowledge as collective intelligence is socially constructed from the common understandings of people. It works as a filter for selecting highly regarded information with collective annotation based on bottom-up consensus and the unifying force of Web-supported social networks. The rising interest in harnessing the collective intelligence of Web users entails changes in managing the knowledge of individual users. In this paper, we introduce a concept of knowledge management based on harnessing the collective intelligence of Web users, and explore the technical issues involved in implementing it.