Remember that polls are snapshots in time and are not meant to be predictive of the final result, especially those that are taken very early (as Presidents Thomas Dewey and Michael Dukakis can attest). Campaigns can use polls as reference points in deciding how/where to invest political resources, but they should not be interpreted to mean "Candidate X is all but certain to win/lose" unless the margin is well outside the margin of error.
A counterpoint to this is that the electorate is clearly a lot less fluid and open-minded than it used to be. Dewey and Dukakis had big leads a matter of months before the election. Hillary Clinton and Joe Biden were never heading for a 40+ state landslide at the equivalent points.
Having said that, this also means that it's pretty likely that a given election will remain at the very least competitive.
