While the popularity of business communication on sites like Twitter and Facebook is growing as a marketing tool, the majority of tweets or posts remain personal in nature. People communicate in a way similar to text messages except public messages appearing in the mainstream are viewable to all. Twitter in particular operates with an open door policy: anybody can read any tweet on twitter unless the user has opted to "protect" his account. Those are still public, published on Twitter but then those persons are free to ("retweet") the messages as they wish.
This has become a hotbed of evidence utilized not only in criminal prosecutions and their defense, but in family law cases, dependency cases and more. People are not realizing the extent to which a tweet or post can be used against them. Many times people come in with screenshots of posts or tweets that have since been removed. So simply deleting your posts or tweet doesn't always solve the problem. Even employers are screening people based on their social media activity or posts. Keep that in mind when engaging in social media activity because anything you say, tweet, or post, could be used against you in a court of law.