In general it's hard to know what a chunk of the pie chart means. You get a very simple glance that one chunk is bigger, and another chunk is much bigger. But looking at that chart: How big is Eclair & Older compared to Honeycomb?
That chart is ordered by release; you start reading it at "3 o'clock" on the right hand side, and work clockwise.
Luckily they've labled each chunk of the pie. Normally they'd just have a key alongside it. People would have to match a shade of green (or some other color) to a key to try to get the numbers.
Pie charts do have uses. But they're just hard to read and present information in a weird way.
It's very hard to judge the relative size of various wedges, especially when they're not adjacent and one is significantly larger than the other.
Secondly, the labels are usually sufficiently removed from the data that you need to look back and forth several times to decode it, if you can even be bothered.
Pie charts are stupid because the shapes you want to compare are rotated in space. You can't distinguish close values. It's better to use a normal bar/column chart where the comparison only occurs in one dimension (height of the bar).
