Modern dictators fear three things: Eagles in the white house, the muslim brotherhood on the streets and twitter. Social media have undoubtedly had a strong impact as a catalyst of change.
What they didn't do is start a revolution by themselves, guarantee success or warrant a lasting change. We can't say that revolution is the new meme or that the recent events in North Africa and the Middle East would not have happened without social media.
What Twitter e.a. did do was make journalism a lot more personal. A nice politically correct editorial is to a tweet from the streets what a gentle tickle is to a punch in the face. Retweeted messages from people fighting and dying have made a very strong impression on me these past few weeks.
It will be interesting to watch special interest groups jump on the bandwagon and say, "Hey, what the Libians do to Ghadaffi we can do to fur!", trying to rickroll themselves a revolution by spamming PETA fursnufftubes. However, I don't think that is very effective. I feel engaged by a people's cries for freedom, but not necessarily by a hippie with an iPhone (oh the irony) spamming me for the cause.
In short, social media are a great conduit for personal and powerful messages. However, this is an emergent effect determined by the sympathy of the audience. Social media by themselves are not a panacea for instigating change, and trying to force their effect will most likely trigger a mass unfollow.
