In watching this long campaign, it is clear that one's performance is much less important than one's performance relative to expectations. Obama's victories in VA, DC, WI and others in the primaries, while huge, did not change the tone of the campaign because his big victories were expected. Hillary's HUGE victories in WV and KY were similarly meaningless. Sarah Palin "won" the debate with Biden by not crapping all over herself in a fit of panic.
If Barack Obama is going to do any of the things he's campaigned on, whether specific policy proposals or changing the tone in Washington, he will need to put up a big win. 270 is of course the magic number, but if he only wins, say, Kerry plus VA, IA, CO and NM, for a total of 286, many will interpret his victory as a squeaker, a failure of Obama to close the deal, and a reaction to all the "socialist" talk in the last weeks of the campaign. Even with 56-59 Dem Senators and a majority in the House, it will be difficult to reform health care, expand education funding, or anything else without an obvious mandate.
So this is why, despite my 100% confidence that Obama will win tomorrow, I will be out knocking on doors for Obama in Pittsburgh all day tomorrow (pushing the start of the liveblog back to 8ish). And to all my readers in Ohio, that's a vital 20 EVs. Anything with a 3 in front of it is immeasurably better than anything with a 2, and Ohio could very well be the difference. Obama wins in Ohio and Florida pushes McCain perilously close to something starting with a 1. In the perception game, that's a big deal. So get out and vote, and when you're done with that, call all your friends. Maybe knock on some doors. It's important.