Here is some fascinating research out of RPI where a team has constructed a model for how ideas spread:
Scientists at Rensselaer Polytechnic Institute have found that when just 10 percent of the population holds an unshakable belief, their belief will always be adopted by the majority of the society. The scientists, who are members of the Social Cognitive Networks Academic Research Center (SCNARC) at Rensselaer, used computational and analytical methods to discover the tipping point where a minority belief becomes the majority opinion. The finding has implications for the study and influence of societal interactions ranging from the spread of innovations to the movement of political ideals...
This model appears to be in its infancy, but it might be worth following their work. Whether we are headed for a massive contraction and descent into negative mood, or we somehow muddle through this current economic malaise for one last big bull run, how ideas spread will be important.
This has huge implications for everyting from advertising to terrorist operations. Be mindful of the memes circulating in your particular part of the globe.