"It has been said that something as small as the flutter of a butterfly's wing can ultimately cause a typhoon halfway around the world." - Chaos Theory
A recent and remarkable example of such a disproportionate effect came from Tunisia. A municipal inspector slapping a Tunisian fruit seller on December 17th 2010, triggered the set of events which eventually led to the tumbling of two regimes in Middle East, and third (Libya) in a state of deep unrest.  Links - NYtimes, Economist (Audio)

Another example where a single Tweet on the ownership of IPL Kochi from @lalitkmodi eventually triggered the exit of him from IPL and @shashitharoor from from cabinet.

And more recently, a strong anti-semitic comment from designer John Galliano has brought serious repercussions for the house of Christian Dior ($28.5bn revenues in 2010). 
"I Love Hitler ... ..." - John Galliano - YouTube link, Story link.
Even though Dior has sacked Galliano, the implications are still hard to predict. Another butterfly-effect may quickly damage their brand and business.

We are only beginning to see the disproportionate effects triggered and accelerated by the power of digital media (YouTube, Twitter, FB etc.). These are only three examples.