In 2004, nationally, George W. Bush and John Kerry were tied most of the summer until Kerry pulled ahead in August with a convention bounce that disappeared by September. In the Fall the two were either tied or Bush was slightly ahead. Obviously Bush won. In the summer of 2000, Bush led early on, then Gore caught up, and it became historically close.
So it's 2008 and the national polls show it close but Obama remains slightly ahead (48% to 41%). Does that matter?
The real election is a set of smaller state elections that decide the Electoral College, so national polls numbers are misleading. Plus Obama has been locked in a newsmaking battle with Hillary Clinton while McCain campaigned in obscurity. Apples and oranges, this early on.
What people know about the campaign often comes from election polls, which are terrific barometers of what's happening, the effects of real-world experiences, lousy economic conditions, and personal foibles by candidates and their respective pastors (or ex-pastors, or former pastors, or religious confidantes, or whatever). Enjoy the polls. They make great party discussion fodder. But never use a general national poll as guidance of how all the various red and blue states will break on election night. National polls are a snapshot of national thoughts, and a fuzzy one at that. Fun, fascinating, illuminating, but not all that predictive when it gets down to state-by-state battles.