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.
But here's the important part: None of this should stop you from blogging. Freedom of speech is the foundation of a functioning democracy, and Internet bullies shouldn't use the law to stifle legitimate free expression. That's why EFF created its Legal Guide for Bloggers, compiling a number of FAQs designed to help you understand your rights and, if necessary, defend your freedom.