One can only cheer at the news of Google's decision to index the contents of the world's biggest libraries. It will undoubtedly revolutionize academic research in the humanities, rescuing obscure texts, and making it far easier to assess the scope of certain themes and topics. In my own research on modernization theory, one of the main tools I used was JSTOR, an ever-expanding index of key American academic journals, dating back in many cases to the nineteenth century, which allowed me to track quite precisely the radical transformation of the idea of "modernization" from the first to the second third of the twentieth century.
However, a small precaution: Google's efforts may enable lazy researchers to rely monolithically on keywording as a research methodology. If this takes place -- that is, if academics allow their undergraduates to do this -- it will represent a withering of important research skills and a truncation of historical sensibility. One invaluable research habit, as I discovered in my own work, is to walk through the aisles of a library and look at the other books filed next to the book you originally sought. Likewise, when doing historical research, one helpful way to contextualize an old article in an newspaper or magazine is to read other articles that appear in the same issue or week -- to help get a sense for the overall structure of sentiment in which a given topic was being discussed.
In other words, if relied on exclusively, keywording risks divorcing words from the wider contexts in which they initially appeared. And dematerializing and decontextualizing texts in this way cuts readers off from a key source of textual meaning. The point is not that Google's indexing is a bad thing: it's absolutely not. But it does give lazy researchers the rope with which to hang themselves.