Jack Balkin has a great summary of the 9th Circuit's recent Batzel decision (PDF) and its implications for bloggers:

This does not mean that bloggers are immune from libels they themselves write. It means that they are immune from (for example) libels published in their comments section (if they have one) because these comments are written by other people and the blogger is merely providing a space for them to be published. Congress wanted to treat operators of chatrooms and other interactive computer services differently from letters to the editor columns in a local newspaper.

So if bloggers defame somebody, they can still be sued for what they say, just not for what someone else who publishes on the blogger's site says. The Ninth Circuit extends this immunity to people who run e-mail lists and republish the e-mails they receive to the list, even if they edit the e-mails a bit or do not republish every e-mail they receive. That is different from the rules that apply to print journalism. A newspaper is responsible for defamation in letters to the editor or op-ed columns that are published in the newspaper. [Bag and Baggage]