If your blog is available for public viewing, you are bound to follow journalistic laws. When it comes to the law, not knowing that something was against the law or unacceptable is not a valid excuse. You have a responsibility to ensure that everything you are doing on your blog is legal. You can get sued, and possibly fined, for what you put on your blog. While there are many legal issues concerning blog posts, the ones that you need to be most aware of are defamation, the use of intellectual property, trade secret laws, and privacy laws.
Defamation: Defamation is the act of publishing something that is not true about someone else, but defamation is also the act of publishing something about someone that causes harm to their reputation, even if it is true, if you were not privileged to say or publish the information.
In light of this definition, you may think that it isnt okay to publish anything about anyone, without the possibility of getting sued, but that isnt quite true. If what you are publishing is the truth, and it can be proven, then you can publish it. However, if it is just your opinion, and there is nothing to prove that opinion, you might get sued if the statement could hurt the persons reputation in anyway. However, you can make a statement about somebody and make it clear that the statement is just your opinion, based on your own knowledge or observations.
Usage of Intellectual Property: You are subject to copyright laws. This means if it is copyrighted, you cannot use it on your blog without making sure that you get the proper permission, or at the very least give credit to the original author. However, if you are just giving credit to the author, and not getting permission to use the entire work, you can only quote small portions of the work, and you still must give credit to that author.
Trade Secret Law: If you worked at a restaurant that has a secret recipe, it is illegal to publish that recipe if it is trademarked or copyrighted. This is an example of breaking the trade secret law, and you can be sued for doing this type of thing.
Privacy Laws: We all enjoy the right to privacy. Therefore, it is illegal to publish private information about a person without their permission. For instance, if you know your neighbor had a sex-change operation or that they are gay, it is illegal to publish this information. Likewise, it may be illegal to publish personal factual information, such as someones social security number.
If you are going to write something negative about someone, make absolutely sure that you find out if publishing such information is legal or not. If you dont, you could find yourself in court, paying restitution. While you should feel free to blog about any topic you want to blog about, when you are using someones name, or writing anything that could make them identifiable to others, remember the golden rule: If you cant say something nice, dont say anything at all.