Before the Thanksgiving holiday, Steve Tobak at CNET published a useful post -- "Bloggers beware: You're liable to commit libel." In it, he gives a straightforward and largely accurate account of the elements of a defamation claim and some good general advice:

Tomorrow we officially launch our Legal Threats Database, a catalog of the growing number of lawsuits, cease-and-desist letters, and other legal challenges faced by those engaging in online speech. As many of our readers are no doubt aware, the individual threat entries have been available for some time, but starting tomorrow users will be able to view the entire database and search the entries using a number of fields, including location, legal claim, publication medium, and content type.