I have yet to see a single example of where a pie chart was superior to any of the obvious alternatives. They are particularly troublesome for those that have less than perfect RGB vision, and even then I often find myself trying to deduce which arbitrary shade of blue is which due to the fact they're sandwiched between two other random colors.

If you wanted to make a chart that looked impressive but contained as little information as possible, you'd have to work to do better than the pie chart.