The National Research Council in the United States has published an excellent report on the Internet.  The focus is on protecting youth from pornography, but it contains a wealth of information.  Details follow:

Youth, Pornography, and the Internet - 2003

Dick Thornburgh and Herbert S. Lin, Editors
Committee to Study Tools and Strategies for Protecting Kids from Pornography and Their Applicability to Other Inappropriate Internet Content 
Computer Science and Telecommunications Board
National Research Council
National Academy Press
Washington, D.C.