ABC, CBS, NBC, CNN, Fox News Channel and The Associated Press pool resources to conduct exit polls in select precincts, hoping to glean information about why people vote the way they do and to help predict a winner or loser. A combination of actual vote counts and exit polls is generally used to "call" a state for one candidate or another.
Exit polls frequently overstated Obama's vote during the primaries by as much as 3 percentage points.
"We're concerned about it, but not, `Oh, my god, the exit polls are going to be wrong,"' said NBC News analyst Chuck Todd. "We're aware it's an issue and we're doing everything we can to correct it during our survey work."
Well-educated and young voters are more likely to agree to fill out an exit-poll survey, and both these groups have tended to favor Obama, the experts said.
Enthusiastic voters are also more likely to seek out pollsters, or at least not go out of their way to avoid them. That was true about Obama during the primaries, just as it was for Republican Pat Buchanan during the 1992 New Hampshire primary, said Kathleen Frankovic, CBS News director of surveys.
It was the exit polls' overstatement of John Kerry's support in 2004 that caused problems for the networks, particularly when the first wave of results were leaked on the Web. That led to a "quarantine room" reform that will be in place this year; the people with access to poll results are locked away until at least 5 p.m. EST, giving them time to check for any problems and keeping the early numbers from conveying false information and possibly affecting turnout.
The problems were more serious in 2000, when networks prematurely "called" Florida, and thus the election, for George Bush. It led to a congressional investigation into their practices.
For the Obama-McCain contest, there's concern about whether some voters will say they voted for Obama but, for racial reasons, actually didn't.
Frankovic said this was a real issue for pollsters years ago, but studies show it has virtually gone away. The false reporting was more pronounced when voters were actually interviewed by pollsters, but the current exit poll is a paper survey that voters fill out in private. It was only in the Northeast that Todd said he saw false reporting problems during the primaries.
A presidential election with a black man leading the ticket is uncharted territory for the United States, however.
In general, Republicans tend to be less enthusiastic than Democrats about taking exit polls. An unknown this season will be whether resentment toward the media fomented by John McCain's campaign will make his supporters even less willing to "help" them by taking a survey.
The smallest of factors can play a role in the makeup of a poll; some older voters, for instance, are uncomfortable dealing with young pollsters, and are turned off if they're standing near partisan demonstrators. News organizations this week sued the state of Minnesota to block a state law that would keep pollsters more than 100 feet from a polling place.
Simply knowing all of this will help the news organizations be ready, the experts said.
"I wouldn't overstate the concerns," said Dan Merkle, decision-desk director for ABC News. "They are the kinds of things we've seen before with different elections and different candidates."
Kathleen Carroll, executive editor of The Associated Press, said she's aware of the issues but isn't worried about the Election Night performance. In states where a race is close, the AP relies on vote counts to pick a winner, she said.
"The AP has never run out and called a close race based on exit polls," Carroll said. Where they can be used to make a call is when the exit polls confirm pre-election polls in contests that are lopsided, she said.
Todd said there's been some notable successes with the exit polls this year. For instance, they precisely forecast Hillary Rodham Clinton's surprise win in the New Hampshire primary, something pre-election polling did not, he said.
People focus heavily on the exit polls' forecast of winners and losers and tend to overlook the greater value, in providing insights on what a population is thinking politically, he said.
"Anybody who just goes off exit polls is a fool," he said. "It is a part of the process, but it is not the process."