It can play a big role in developed societies ( Western Europe or North America ) but in developing societies the digital divide is huge. How do you reach out to those who have a limited idea or absolutely no clue about the digital world? Can you twitter away in Afghanistan? In Iran the "twitterers" are few and far between... People who twittered in Iran may not have the influence to mobilise or shape the ones that matter. The lower classes and the poor form the basis of Ahmedinejad's support courtesy his "populism."
In India for example the 700 or so odd millions that do not have access to the internet decides policies by the power of their vote. This recent election is a good example .. so was the last one. The well-off, the middle class, the internet users are apathetic to use thier vote anyway.
As a communications consultant I have found that whenever I was confronted with the problem of communicating in a diverse and class ridden society the radio has always delivered. Social media has its advantage in being "uncontrolled" but its disadvantge lies clearly in being able to target a select group only. It however remains a great tool for planning and organising. Only time will tell how the medium evolves in areas like South Asia, Middle east and Africa, Asia-Pacific etc.