I just read a terrific analysis of this year's presidential electoral map from Al Giordano. In short, it's really, really tied and the single thing that will decide the election, even more than normal, is likely to be the ground game.
As the article states, "the 2008 presidential election is about registering those voters mentioned above, and getting them out to vote. Period. End of story. Little else matters."
If you have a strong opinion about the next President, be it McCain or Obama, and particularly if you live in a battleground state (Virginia, Florida, Pennsylvania, Ohio, maybe Mississippi), it really might be worth your time to volunteer locally.