The Electronic Frontier Foundation has published a Legal Guide for Bloggers, a list of FAQs that look at the liability issues facing bloggers:
Whether you're a newly minted blogger or a relative old-timer, you've been seeing more and more stories pop up every day about bloggers getting in trouble for what they post.
Like all journalists and publishers, bloggers sometimes publish information that other people don't want published. You might, for example, publish something that someone considers defamatory, republish an AP news story that's under copyright, or write a lengthy piece detailing the alleged crimes of a candidate for public office.
The difference between you and the reporter at your local newspaper is that in many cases, you may not have the benefit of training or resources to help you determine whether what you're doing is legal. And on top of that, sometimes knowing the law doesn't help - in many cases it was written for traditional journalists, and the courts haven't yet decided how it applies to bloggers.