Social media can indeed be a very powerful tool if used correctly, unfortunately it can also be devastating if used badly as demonstrated by Ashton Kutcher. I actually heard about this from Doc Sheldon, a fellow SEO who saw the whole thing as it happened.
Kutcher had heard about the sacking of Penn State's football coach Joe Paterno. Unfortunately he had not heard that he was fired due to his failing to act over alleged child abuse by long-serving assistant. Kutcher hit twitter and made his feeling about the sacking known before he knew all the details.
As you can imagine there was quite a backlash as Kutchers 8 million fans turned on him. He attempted to repair the damage replying to as many people as he could to apologise and explaining his mistake.
As Doc points out in his blog post: Feeding Frenzy on Aston Kutcher he would have been far better to write one tweet apologising and explaining his error then leaving it alone. In the end he sent one final tweet saying he was going to stop using twitter until he could figure out a way to manage it properly.
Ashton Kutchers has since removed most of his tweets apart from the last open apology but his mistake demonstrates what can happen when you don't have all the facts before you say something on twitter and also how important it is to know what to do when it goes wrong.