Bullies at the Voting Booth: "What if Republican shenanigans tip the election? Many members of the media are looking at the dangers voting machines may pose to the integrity of the national election. Others are wondering whether voters may be disenfranchised by use of faulty felon lists, as happened in Florida in 2000. But there is another danger: Republicans may use a variety of tactics to suppress the vote of racial minorities in swing states. These tactics could determine control of the White House or the Senate."
This one points to more dirty tricks by Republicans than by Democrats, and that makes me somewhat suspicious. However, here's a guide to disenfranchisement, machine style.