Arab spring for now, but what if dictators and anarchists learn to use Social Media effectively?

Recently, an innumerable numbers of articles, blog post and, more generally, discussion has revolved around Social Media's potential in bringing about political and social change to the masses. But what about its potential to control the masses through disinformation? What about its potential to generate social instability for dubious purposes?

Granted, there yet few examples of this dark potential as of yet. Or at least that is the perception of people that are on "masses" side of the disinformation campaign.

I'm not trying to create conspiracy theories, I actually do have an example of a case in my country which I believe has not been explored enough in a Social Media context. Let me give you the quick overview of the case:

• Rodrigo Rosenberg, a prominent Harvard and Cambridge educated attorney is shot dead just a few block from his apartment in Guatemala city
• A few days later a video of Mr. Rosenberg surfaces on YouTube, recorded less than a week before his murder. In it he claims "If you are watching this message, it is because I was assassinated by President Álvaro Colom, with help from [Colom's private secretary] Gustavo Alejos." Given the level of corruption, drug cartel problems and violence in the country the narrative presented by Rosenberg is actually not too hard to believe, and his death serves as the ultimate evidence
• The day it is posted the video has 80k views, and reaches 150k over the next few days. All hell breaks loose. An already weak leader is faced with widespread demonstrations, attacks from the press, attacks from political opponents and attacks of political allies. The president comes incredibly close to being toppled by his main rivals and by popular demand.
  

So far it looks like the makings of a mini Guatemalan Spring, no? Indeed, that is what it felt like for those of us there (I was in Costa Rica at the time but was there in spirit).

The only problem was that it was all part of a very strange plot. However, this only came out months later after a UN investigation followed all the leads up to the murder. The Colom Administration survived. This is the short version, you can find the long version in a New Yorker article if you are interested (or talk to me).

So back to my main question... yes, social media is great, but are we too much focused on the positives and ignoring the risks? What impact would this have if, say someone carried out a similar, more successful disinformation campaign in a much larger economy (say, the US)? We know Social Media amplifies public perceptions, what if the public is wrong, and the impact of this is large?