ABC News has an excellent piece on the danger posed by ID-matching rules that will be used this November in states across the country, the most recent addition being Florida.

States are matching the names in their newly-developed centralized voter databases against Social Security numbers and other criteria. The problem is that the databases are notoriously plagued with errors. As ABC News reports:

But the databases, some created by the same companies that make electronic voting machines, aren't federally tested or certified and some have been plagued by missed deadlines, rushed production schedules, cost overruns, security problems, and design and reliability issues.

Over 1.3 million voters didn't cast ballots in 2000 because of registration problems. That number could be much larger in 2008 because stricter laws based on databases that are susceptible to human errors:

HAVA leaves it to states to decide how to conduct matches. Some states require an exact match with the Social Security Administration database and only a substantial match with motor records. Others require an exact match for a voter's Social Security number, first and last name, and month and year of birth.

Exact matching, however, could mean that a woman who recently married and changed her name would fail to match government records containing her maiden name. Voters who have double last names or unusually spelled names might also fail. Everything depends on how a state's matching algorithm is designed.

The risk of disenfranchisement isn't theoretical. States have been running simulations where up to 1 out of 5 voters failed:

Last month Wisconsin, whose database just became operational, conducted a test of 20,000 voter names against motor vehicle records and found 20 percent with mismatches, due mainly to typos and transposed numbers. Among those who failed to match were four members of the state's Government Accountability Board, which conducted the test. Thomas Cane, the board's chairman and a retired judge, failed because he was listed by his full name, R. Thomas Cane, in his driver's record.

As ABC News notes, most states will allow you to still vote if you present an ID at the polls. But not in Louisiana and South Dakota. And in Florida, the ID you bring must exactly match what's on the voter list, meaning the possibility for error is huge: in 2006, 13,000 voters were knocked off the lists, and more in 2007.

Defenders of the system say that voters who believe they were wrongly excluded can make their case. But as ABC News points out, the process is so laborious that most will probably end up confused and not voting. Here's what a voter has to do in Florida:

Beginning Sept. 8, new registration applicants who fail a HAVA match must mail a copy or bring a hard copy of their ID to an election office before Nov. 4 to show that the ID number on their registration application is correct. Officials plan to send a letter to such voters explaining what to do. Voters who forget or never receive instructions can cast a provisional ballot on Election Day, but it will be counted only if they bring or send a copy of their ID to an election office within 48 hours. ID presented at the poll will not be accepted, which could create confusion since Florida law already requires everyone to show ID at the polls.

And of course, it has happened before in Florida:

Florida's voter-registration list isn't new to controversy, of course. In 2000 a contractor hired to weed out convicted felons used broad criteria to match voter names against correctional records and swept up thousands of the wrong people. The same problem occurred in 2004.

At this point, the only route for voters to ensure they won't be disenfranchised is to double-check their registration status or call an election hotline number like 866.MYVOTE1 if there are problems.