Another aspect - pie charts beyond about three wedges are utterly useless to the colorblind. The OP's Microsoft example is particularly egregious in that aspect as well - I can't distinguish most of those colors, especially given the minuscule legend. So the entire pie chart is quite literally wasted on me. A blank rectangle would convey nearly as much information.
As a colorblind myself I couldn't agree more. But this is not limited to pie charts, any kind of graphics that uses more than 3 colors to identify labels in a list is completely illegible for me.
>pie charts beyond about three wedges are utterly useless to the colorblind
The problem lies in using a color-coded legend, not in using pie charts per se. The slices of a pie chart can be labelled directly (instead of indirectly via a legend), e.g.,
http://www.fedstats.gov/kids/mapstats/graphics/pie.gif
