Personally, I kind of like pie charts for certain representational tasks. Maybe it's fond memories of the cognitive challenge of selecting which slice of pizza I wanted vs. which one I was going to leave for my brother. I get suspicious of all these quotes about "differences in angles are not easy to judge for the human eye" whenever I'm at a kindergartner's birthday party. Those kiddos don't seem to have a huge problem identifying the biggest piece. Maybe if we called them "cake charts" the experts would relax.
Anyway, I say that in defense of the humble pie chart, because now I'm about to eviscerate one.
I came across this in an annual report for Xcel Energy that I was thumbing through. This lovely little key lime pie chart struck me as so unreadable that I had to cut it out to keep forever.
The unreadability has nothing to do with it being a pie, but it has everything to do with the overly subtle variations in color and the decoupling of the visual from the legend.
I defy anyone to discern the percent of renewable resources. But then again, maybe that's the point.
Hint: look for a tiny (1%) slice headed southwest.