The US military is developing software that will let it secretly manipulate social media sites such as Facebook and Twitter by using fake online personas to influence internet conversations and spread pro-American propaganda.The authorities assure us that this technology (Operation Earnest Voice) would be illegal to use in the US--so why should we worry? See this, this, and this.
On the other hand, there are some skeptics, like myself, who believe that the ruling class clearly saw what happened in Egypt, and are preparing to use social media to manipulate the minds of Americans as they have done so effectively, although more subtly, through their control of education and mainstream media.
Still, many politically astute people believe that we can use social media to organize. Maybe so. In any case, we must be aware of the dangers.