Inspired by James Wood's latest litany of eloquent complaints against the God in whom he doesn't believe, here's something I'd like to see: A history of popular theodicy, tracing the influence of the "argument from the existence of evil" against belief in God (or the Christian God, at least) throughout the course of Western history. It's my impression - and it's only an impression, which is why I'd like to see someone do the necessary intellectual spadework to refute it or back it up - that this argument has gained increasing currency even as our material conditions have dramatically improved; which is to say, the less suffering a particular population experiences, the more likely the suffering it does experience will be cited as evidence against the existence of a benevolent deity. (Or put another way, you're more likely to hear New Yorker writers wax indignant about how the existence of human misery precludes their believing in God than you are to hear the same argument from people in slightly less comfortable positions.)
I can think of various reasons why this might be so. There's the correlation-causation possibility: Atheism in general has become more prevalent as material conditions have improved in the West and science has demystified large swathes of the natural world, and since the problem of evil is one of the stronger arguments for atheism, you'd expect it to be cited more often in a more atheistic age. (Wood gestures at this notion in his essay when he remarks that "nowadays, theodicy always has a wary eye on the theological exit: this makes no sense, therefore I will have to reject the idea of God. But there was no such exit before about 1700, at the very earliest.") Or it could have something to do with mass media and instantaneous communication, which expand (and emphasize, since if it bleeds it leads) the range of tragedies that educated people are exposed to on a daily basis. (Wood opens his essay, tellingly, by reading off a roll of tragic headlines from a single copy of the New York Times.) It could have something to do with the scale of inhumanity that modern technology makes possible: Thus the reasonably-convincing argument, for instance, that the experience of two world wars and the Holocaust has been a crucial factor in Europe's abandonment of God. Or it could reflect something inherent in our psychology, which makes suffering seem like more of an absolute injustice the less we actually experience it.
I don't know the answer, or even if the thesis is correct - but I'd love to see someone investigate the question.