I can't remember the name of the book, but I remember reading that people name babies both after celebrities and after names of the higher class people around them (with the goal of their children appearing higher class than they actually are). The latter case is interesting, because it goes in a cycle - the higher class folks pick unique names for their children, the lower class folks copy them in the next generation so those names become common, and the higher class folks pick new names in the next cycle.

So if the data was there, it'd be interesting to show these graphs both alongside celebrity popularity over time and also to divide the graphs based on socio-economic lines, to see if that is still happening.