[lynaghk]

Stephen Few has an excellent overview of why pie charts should be avoided: http://www.perceptualedge.com/articles/visual_business_intel...

Neither pies nor mosaic charts should be used if you need exact readings of the data --- though mosaic plots do have the advantage of being rectangular, making segments much easier to label with values than the segments of pie charts.

[Gravityloss]

I disagree partly. It's easier to estimate relative shares of a total from a pie chart compared to his linear examples.

[amalag]

I am also not so convinced. I still like a simple pie-chart.