For purposes of this year's presidential election, I normally argue that the only number to really pay attention to is the national popular vote--generally, the electoral college will follow it. Since the two major parties formed up in 1856, there have only been three elections (1876, 1888, and 2000) where the popular vote didn't determine how the electoral college would go. That said, the Obama and Romney campaigns obviously have to concentrate their resources on the "close" states.
Here is a handy tool for your calculations. While polls have shown relatively close margins in over a dozen states, I'll predict that for most of those they're going to fall out of contention in the coming months. Start by clicking the map to "2008", where Obama won last time, and let's work from there:
1) Obama will not be winning any of Nebraska's electoral votes, or Indiana or North Carolina. He got these last time.
2) Romney will not pick up any of the "blue" states in the Northeast--New Hampshire and Pennsylvania will stay blue this year.
3) The questionable states at this point will be: Nevada, Colorado, Florida, Virginia and Ohio--all of which went for Obama last time.
4) Romney will do better in Florida and Virginia than the other three. If he wins Ohio, he'll win the others, and the election. If he loses Ohio, but wins Nevada, Colorado, Virginia and Florida, he will lose. I don't see him losing Ohio but picking up any other "blue" states.
What stands out about this is the closeness of the electoral vote count--gone are the days when the winner handily blows out the loser. In Bill Clinton's victories, for example, he had a number of southern states to pad his lead, and in the Republican victories before that it was normal for the winner to take California, most of the midwest and even a number of northeastern states. (This of course reflected a time when conservative Democrats and liberal Republicans existed in enough numbers to make a lot more states competitive).
The unfortunate takeaway? Not just the fact that the candidate who wins this is going to have about half the country bitterly opposed to him and his policies--at a time when compromise will be necessary to figure out how to stimulate the economy, reduce the deficit and determine the American role in the world. But also this means ideology is far more determined by geography than any time in recent history.