But some of these snap polls or focus group polls immediately following the debate are based on a much smaller sample.

The Gallup and Rasmussen tracking polls use about 3000 and take a 3-day weighted average.

Realclearpolitics has a great "poll of polls" where they take the average of all the polls in the past week or so, therefore giving you results based upon a sample of about 15000. It currently shows Obama with a 6.3 point lead.

The Intrade market prices have swung heavily in favor of Obama this week too, and stands at about 80% - 20% right now. This would indicate that even many, perhaps even most, who support McCain no longer really believe that he's going to win...