It turns out it's a whole lot easier to get amped about an election where your side is likely to kick butt than one in which it looks like your butt will be kicked. This has, I think, as much a role in the enthusiasm gap as anything. And while my sense is that most people reading a DailyKos diary are going to vote, it's worth laying out the case for why it is so damn important, particularly in this year.
There are lots of predictions of Republican gains in the election: Nate Silver thinks they'll win the house, and gain a bunch of seats in the senate. That seems to be the consensus prediction, and since the consensus is so robust you may feel it's a fait accompli. It's not.
This is an obvious point, but one worth remembering, particularly for the many poll junkies who I'm sure are reading this: Better models for predicting electoral outcomes do not mean outcomes are more foreordained than ever. The first reason to vote is the most obvious: the future is not yet determined. Turnout matters a great deal, and there are dozens of elections around the country that are going to be decided by razor thin margins. Tom Perriello won his 2008 race against Virgil Goode by a mere 700 votes. Al Franken (about whom more in a minute) defeated Norm Coleman by the preposterous margin of 312 votes out of more than 2.8 million cast!
And not only did those 312 votes gain Franken a senate seat, they also gave the Democrats (after onerous litigation) a fleeting, but important, 60 vote majority in the senate.
Which brings me to the second reason to get out and vote: margins matter. Even if Republicans win the house and the Democrats maintain control of the Senate as nearly everyone is predicting, the margins in both houses will be incredibly important. Remember that Republicans accomplished a tremendous amount of damage by keeping Al Franken out of the Senate. That was just one senator. Remember that the most significant pieces of domestic legislation of this last congress -- health care, financial reform, the recovery act, all passed by razor thin margins. A few votes in the other direction and none of it happens. Just because control of the house might change, doesn't mean that the last vote on a important piece of legislation (immigration reform for instance) won't be just as important. When you go out to your polling place, you have a chance to be electing that last crucial vote.
Our system is not a winner-take-all system, as we learned sometimes to our frustration over the last two years. If enough people get out and vote tomorrow, there's going to come a time in the next two years when Republicans are just a few votes short of getting something they really want, something that would be genuinely awful for the country. You're the last defense.