Honest question here (and I hate how I feel compelled to preface with that): In what situations are the "circle stats"/circular representation of a bar graph useful? Aside from its aesthetic appeal, it doesn't seem very functional.
To be honest, I think gauge like controls/graphs have become so popular on dashboard because their physical world counterparts all featured gauges. Check the dashboards of an airplane or nuclear facility for example.
You could call it skeuomorphism if you want. (http://en.wikipedia.org/wiki/Skeuomorph)
However these gauges at the top are not replacing a bar chart, as they each only show one value in isolation - that'd be a pretty simple bar chart. When you're showing one value, and at most might have targets to show in relation to it, a radial chart is just as good IMHO, and lets you put other info in the centre (like the figure in numerals for example). The closest tabular representation would be the weekly stats at the bottom.
I think they make a nice compliment to the other graphs on the page, and do not sacrifice usability for aesthetic appeal given that there are other styles of chart used where appropriate (for example the time series of visits etc.).
http://en.wikipedia.org/wiki/Pie_chart#Use.2C_effectiveness_...
> Further, in research performed at AT&T Bell Laboratories, it was shown that comparison by angle was less accurate than comparison by length.
Also, my guess is that speedometers are circular because of technology available at the time first cars were built. I think I'd much rather see a bar as a speed indicator. I guess it could be tested; anyone knows any racing game which allows to switch between standard speedometer and some kind of speed bar?