Well, huh! Turns out you can chart by Time Zone, too, as below.
Although I'm just using a simple pie-chart, this opens up some interesting possibilities around adoption (e.g. thinking "stacked chart", could do "last login week by time zone", "license type by time zone", "documents uploaded by time zone", "open issues by time zone"...craziness).
Well! That was a particularly inspirational coffee; but I'm way off task, so I'll leave it there for others to imaginate.
Regards,
Doug