In his wonderful book,Visual Explanations: Images and Quantities, Evidence and Narrative, author Edward R. Tufte argues that, had data correlating launch temperature and O-ring damage been properly presented, the Challenger disaster may have been averted (pgs. 39-53). Instead engineers missed the fateful relationship. This oversight was largely the result of graphical presentation that should have made an obvious pattern stand out, but didn't.
Little drawings of 48 rockets marked with O-ring damage history seemed both clever and appropriate, but added "visual noise". This noise robbed the graphic of it's most critical element - clarity. The sad results of this oversight are history.
In another example from the same book, Tufte discusses the 1854 cholera epidemic in London that caused 616 deaths. According to Tufte, "Dr. John Snow (Queen Victoria's anesthesiologist) was able to discover the cause of the epidemic and bring it to an end". Acting on the effective graphics he'd developed, he devised a simple solution. He removed the handle from a Broad Street water pump, halting the spread of the disease.
But how could quality graphical presentation have have helped with more recent problems? Consider the June 17, 2009 article Use Heat Maps to Expose Rare but Dangerous Frauds by Toby J. F. Bishop & Frank Hydoski in the online edition of Harvard Business Review. The authors argue that simple to comprehend "heat maps" may have exposed events like "the rogue trading in 2007 that cost Société Générale more than $7 billion or the recent Madoff case."