The tech website Gizmodo recently posted an article  that displays the data for the most popular photos of the year.  It examines what cameras they were shot with and the settings that were used to shoot them.  Unfortunately, this is a classic example of interesting data that was displayed poorly.  An example:

As you can see, it’s nearly impossible to understand the data and proof that pie charts are an ineffective way to present data.  In a downloadable article you can access here, Stephen Few explains:

Graphs are useful when a picture of the data makes meaningful relationships visible (patterns, trends, and exceptions) that could not be easily discerned from a table of the same data.

Psychophysicist Stanley Smith Stevens developed what is known as Stevens’ Power Law and states:

the perceived area is usually equal to the actual area raised to an exponent of about 0.8, times a scaling constant…In contrast, relative line length [such as the lengths of bars] is perceived almost perfectly, provided that the lines are oriented the same way. (Kosslyn, Stephen, Graph Design for the Eye and Mind, Oxford University Press, 2006, p. 40)

In short, save the pies for eating.  Next time serve up a tasty bar chart.