Google's Ngram machine
This is fun: check out Google's new Ngram machine, which lets you graph the incidence of words in Google's books archive going back centuries, and also to plot the incidence of different words against each other.
I don't know how accurate it is as a barometer of public interest, but you can see, for example, the rise in the use of the word 'economy' over the last 200 years:
While the use of the word 'wellbeing' has risen over the same period:
And, while mention of God has been sinking since 1800, mentions of 'sex' have been rising - so I guess we've found some consolation in the Twilight of the Gods: