While the presidential candidates are still doing their dances, it's interesting to see how they use datamining for improving their stance: The candidates apparently use companies that mine their voter databases in order to "micro-target" voters via ads and the like. See this blog posting on The New Republic-- courtesy of former student Igor Nakshin. Note also the comment about the existence of various such companies that tailor to the different candidates.
It would be interesting to test the impact of this "mining" on actual candidate voting and to compare the different tools. But how can this be done in an objective manner without the companies actually sharing their data? That would fall in the area of "privacy-preserving data mining".