It strikes me that the thousands of blogs like this one will make a fantastic resource for future historians. With the thoughts they contain, and the metadata that accompanies them, statistical analysis of the notions held by many thousands of people will allow a far more accurate social history than is possible for any other age.
The problem will be that, for now at least, it will only offer a statistical analysis of tech-savvy people, predominantly in economically developed countries. All this assumes, of course, that there are future historians, or a habitable planet for them to live on.