Copyfraud : Poisoning the Public Domain is an introduction to some of the ways that content providers (websites, publishers, etc.) abuse copyright protections when they use public domain materials.  A couple of minor points, however:

• The act of assigning a copyright to something already in the public domain is the issue; taking a Project Gutenberg text, formatting it, and publishing it is of great benefit to people, as long as one doesn’t claim protection that doesn’t actually exist for the material.
• The Creative Commons Public Domain Tools is not a license, nor is it  an attempt “to become the arbiter of  public domain licensing”, but a way to allow people to have an easy and effective way to display that a work belongs to the Public Domain.

found via LISNews