Walter Mebane and David Dill have written a working paper, Factors Associated with the Excessive CD-13 Undervote in the 2006 General Election in Sarasota County, Florida. Here is part of the introduction:

Based on statistical analysis of detailed electronic ballot and event log data from the Sarasota general election ending November 7, 2006, we find that none of the many theories advanced so far to explain the extraordinarily high undervote rate in the Florida Congressional District 13 (CD-13) race adequately account for systematic covariations between that undervote and other identifiable factors, such as voting patterns in other contests and unusual events on the voting machines. At this time, we are unable to propose a convincing mechanism based on voter, machine or ballot characteristics that completely explains the phenomenon.
This paper describes the data and statistical analysis we have performed and evaluates explanations that have been advanced by others as well as plausible explanations that we propose in light of our analysis. Our results are suggestive but in important respects puzzling. In a nutshell, the excessive CD-13 undervote rate in Sarasota County is not yet well-understood, and will not be understood without further investigation. On its own, further statistical analysis of the kind of data we examine here probably cannot explain the undervotes.

This one is very much going to be worth reading, especially given that it reaches contrary conclusions to the other major work out there so far, this draft by Michael Herron and his co-authors.