Immediately after I created the Facebook friends heatmap, I started to develop a craze for creating heatmaps. I made a similar one for the Charlie Bates Solar Astronomy Project. It displayed the location of their members who participated in the International Sun Day. You can see that here.
I also went ahead and used the publicly available earthquake database to plot all the earthquakes since 1990 to create a heatmap. As expected, all of them fell on the tectonic plate boundaries and I was also able to see the most affected parts.