The W3C’s Platform for Privacy Preferences (P3P) provides a standard way for web sites to communicate about their privacy practices (see http://www.w3.org/P3P/ for more details). More and more companies like Microsoft, IBM, Dell, Yahoo, CNet, DoubleClick and many others, are implementing P3P to demonstrate corporate leadership on privacy issues, and, as a positive benefit, prevent IE 6.0 and some other browsers from blocking their cookies (see Internet Options -> Privacy tab).
What is in a P3P policy? Company name and contact info, the types of collected data, how the collected data is used, mechanisms for resolving privacy disputes, etc.
http://www.w3.org/P3P/usep3p.html is a great site with information on how to make your web site P3P compliant, including P3P guiding principles document, links to P3P policy editors, and more.