ISWC2009 Tutorial on Legal and Social Frameworks for Sharing Data on the Web http://www.opendatacommons.org/events/iswc-2009-legal-social-sharing-data-web/
We believe that dedicating data to the public domain is the best way to ensure that data is universally reusable and remixable. When data is public domain it means that it can be reused automatically without needing to check terms and conditions or track the source of every statement to provide attribution. These kinds of things act as friction to reuse, wasting energy that could be better spent creating inspiring things.