Michael Herron sent me this article-in-progress by Jonathan Chapman, Jeffrey Lewis, and himself on residual votes in the 2008 Minnesota Senate race. They conclude:

In the Minnesota Senate case there is no doubt that the number of residual votes dwarfs the margin that separates Coleman from Franken. We show using a combination of precinct voting returns from the 2006 and 2008 General Elections that patterns in Senate race residual votes are consistent with, one, the presence of a large number of Democratic-leaning voters, in particular African-American voters, who appear to have deliberately skipped voting in the Coleman-Franken Senate contest and, two, the presence of a smaller number of Democratic-leaning voters who almost certainly intended to vote validly in the Senate race but for some reason did not do so. . . . At present, though, the data available suggest that the recount will uncover many of the former and that, of the latter, a majority will likely prove to be supportive of Franken.