Facebook was originally made so people could strengthen their relationships by communicating with their friends even if they were far away. Recently, studies have shown that people with low self-esteem have been updating negative statuses, leaving awful comments on their friend’s pictures, and writing terrible things on their walls for everyone to see. People with low self-esteem are more likely to like Facebook because it gives them the opportunity to confront someone without coming face to face with them. They would rather say the rudest things to them on Facebook rather than in person. People with a high self-esteem who post positive things on Facebook are liked better than people who post negative things. People write their negative comments on Facebook because when they say it out loud, they can tell that other people get tired of hearing it. When you use Facebook, you don’t usually see their reactions.
I think that the worst thing in facebook is the privacy, "Good Privacy" is not really a term associated with social networking, especially with a giant like Facebook that is considered to be the backbone of social networking. Be careful about what you post as a status update or on another person's wall. Double check your privacy settings to see what information is available. Applications and other users can take advantage of you if you are not cautious enough.
The second worst thing is the Unwanted Information, You would like to keep your Facebook use to a minimum but your friends are constantly sending you requests to join them in social games, or sharing information that is really better kept a secret. There are options to hide or block applications or users, but new applications are always popping up to take their place.