The differences between Obama/Biden and McCain/Palen could not be more stark.
Something isn’t right about these polls.
I submit that the margin of error may be a lot larger, by factors of two or three or more, than the statisticians say they are.
Gallup's polls fluctuate a bit more because it comes closest to using a scientifically reliable methodology. The truth is that the sample sizes that pollsters use are too small to avoid such fluctuations. Most other pollsters attempt to hide this fact by playing games with the raw numbers (e.g. weighting by party affiliation, which usually means oversampling Democrats -- the favorite Jedi mind trick of media polls in order to inflate Obama's numbers). Gallup weights its polls only by general population demographics, although it does ask respondents questions regarding their ideology as well and publishes this information on a weekly basis at its website.
As for who is actually ahead, these Gallup polls are of registered voters. Gallup has recently posted an article noting that its likely voter samples tend to be about 4 points more GOP than its registered voter samples. This was certainly true four years ago, in what was historically one of the highest turnout elections on record.
Interesting analysis.