A website's privacy policy is usually part of the Terms of Use. Generally, by using a website or web tool you are implicitly accepting the terms of use. The two most important things to know about a Web 2.0 tool, such as a blogging tool or a wiki are 1) how your privacy is protected and 2) who owns the content that you create with the tool.

Example:

Wikispaces Classroom (the host for this wiki) is an example of a web tool with a privacy policy and terms of use that are completely appropriate for use in a school. The Terms and Conditions restate the site's compliance with COPPA and include their privacy policy - they share no data. Because users are producing the information, the site is not responsible for personal information that users publish, which is standard.

In Wikispaces Classroom, the owner of the wiki has complete control over who can view the wiki (completely private, public, or viewable by select individuals) and the owner retains all rights to the content; if the Wiki is made public, Wikispaces encourages the owner to make the content reusable under a Creative Commons license.