Those pie charts are basically useless.<p>They might be better represented as a <i>tag cloud</i>[1], with the most popular keywords given the most prominence.<p>[1]: <a href="http://en.wikipedia.org/wiki/Tag_cloud" rel="nofollow">http://en.wikipedia.org/wiki/Tag_cloud</a>
Data goes all the way back to 2009 and is limited to SEOmoz's blog section alone as I couldn't extract the remaining.<p>Paints a rather interesting picture if you look into their rebrand period etc.