Mark Blumenthal has a very good warning for all of us tonight: Ignore exit polls.

As Blumenthal explains,

“[T]he initial results of the exit poll interviews have had frequent problems with non-response bias, a consistent discrepancy favoring the Democrats that has appeared to some degree in every presidential election since 1988. Usually the bias is small, but in 2004 it was just big enough to convince millions of Americans who saw the leaked results on the Internet that John Kerry would defeat George W. Bush. It didn’t work out that way.”

Exit polls may not be great at head-to-head horse race information, but they still serve an important purpose: Providing us with demographic information.

Because votes are cast anonymously, exit polls can provide us with clues about which types of voters are supporting which candidates. For example, exit polls showing that Romney is losing the female vote by just 2 or 3 points would probably lead one to extrapolate that he will win. What is more, they also provide us with key information for evaluating a race retroactively.

Still, there will be intense temptation for us to tweet and discuss exit polls this evening before any real results come in. After all, we have to fill time and space and provide content.

People who draw any conclusions from these preliminary surveys run the risk of ending up with egg on their face, but there are even larger potential consequences.

A worst-case scenario would be discouraging and deterring voter participation.

Let’s say you’re a Romney voter who lives in Nevada, and you hear exit polls are showing that Obama is winning Pennsylvania, Ohio, and Virginia convincingly. What do you do? Do you stand in line for hours, or do you just go home?