A new version of this report is located at ProPublica. Includes more detail and a comment from Susan Prosser, Vice President of Industry Relations at DomainTools, about the how the DomainTools "IP Explorer" tool gathers the "C block owner" value.
The new version mostly just adds information, but previous versions of this gist can still be seen at the "Revisions" button to the left. Earlier versions should be considered draft quality.