The potential applications for such a tool are surprisingly large; written works make up the entirety of recorded history, after all. That history might not be entirely accurate, but analysis can still yield some fantastic info. The Google Blog offers a couple of interesting graphs -- Virus vs. Bacteria, which chronicles the massive improvements in science and medicine; and Tofu vs. Hot Dog shows both the growing popularity of vegetarianism, and America's love of cow -- but it's very easy to make your own, telling graphs.
Analog vs. Digital, for example, or America vs. England (compare American English to British English). If you find any interesting combos, leave a comment!