All posts in the topic Defining the Open in Open Data, Open Content and Open Information (Short link)
In addition to the opendatacommons.org site Mark has listed, this site has some interesting comments on open data licencing: http://opendefinition.org/ For comments regarding data licensing (as opposed to content licensing, which is what Creative Commons is primarily intended for) see: http://opendefinition.org/guide/data Cheers, Brent Wood