There have been some information on a couple of really excellent research papers on pie charts released today from Robert Kosara (@eagereyes) and Drew Skau (@SeeingStructure) :
I had, coincidentally, been doing some research of my own on perceptual anchors and how that relates to performance of pie charts versus stacked bar charts in part-to-whole comparisons. It would suggest that pies are not the terrible bad-guy after all. Who knew!
Stephen Redmond is a Data Visualization professional. He is author of Mastering QlikView, QlikView Server and Publisher and the QlikView for Developer's Cookbook