I'd like to second the note from the previous "anonymous" on pie charts: can any reader point to specific citations of studies on pie charts? Note that an experiment showing that, say, people have a harder time comparing angles than lengths is not the same as a study on pie charts. Neither is an essay in which someone guesses that pie charts are bad because people are not great at judging angles or areas.

My intuition is the overall effect of a pie chart comes from a lot of interacting factors and in fact pies can be pretty effective.