The current (August 17/24) issue of The Nation magazine has a good article by Ari Berman titled "The Voting-Rights Counterrevolution" (link). It's excerpted and adapted from Berman's recent book, Give Us the Ballot: The Modern Struggle for Voting Rights in America. It's worth reading.
Berman gives disturbing examples of thousands of people turned away from polling places because their registrations had been canceled without advance notice to them. In Leon County, Florida, in 2000, for example, the elections supervisor went through the state's purge list and discovered that of 697 persons identified as supposed convicted felons, only 33 could be verified. It isn't possible to say what the error rate was in other counties because no other elections supervisor bothered to check. Statewide, voters were purged even if their names only loosely resembled those of felons.
For one example, a man named Will Steen, who had taken his ten-year-old son to the polls to teach him about democracy, was told he couldn't vote because he was a convicted felon. In fact, Steen, a US Navy veteran who has served in the Persian Gulf War, had never even been arrested. His name was confused with someone named "O'Steen." (Voters were deemed felons even when they had a different middle name, race, and even sex from the criminal they were mistaken for.) Steen was told to call the Board of Elections but they never answered the phone. Finally he had to leave without voting.
That same year, many other people were illegally stopped from voting in St Louis, and when a judge ordered the polls kept open an additional three hours to give time to correct at least some of the problems, the Bush campaign managed to get an appeals court to cut off voting after just 45 minutes and about a hundred ballots.
Since then, bogus claims of voter impersonation fraud — the rarest typing of voting fraud, with only a tiny number of known cases (just two here in North Carolina since 2000, for example) — have led to strict voter ID requirements that are no problem for most people but prevent many poor and elderly persons from exercising their legal right to vote. Probably around ten percent of voters lack a government-issued ID that meets the requirements.
(As I've mentioned before, I've heard people say that if you need an ID to get on a plane or pick up a registered letter, why is it so bad to demand a specific ID to vote? Because, in fact, you don't need one of a narrow set of government issued photo IDs to board or plane or pick up a registered letter. They make it a easier, but there are alternatives, as you can verify for yourself at the TSA and Postal Service websites.)