A short note about election polls, which I've been following somewhat religiously for the last few weeks.
Election polls differ in at least four significant ways from actual voting.
First, polls are typically of around 1,000 people or less, which means that at best, they are statistically precise to within plus or minus three percent. This means that a six point difference between 2 candidates may be nothing more than sampling error (i.e., a statistical anomaly).
Second, polls tend to be of the general population and not of likely Electoral College votes, which is how the election is counted (but see
electoral-vote.com for a count of Electoral votes, according to polls). As we know from recent elections, the Electoral vote percentages frequently (and seemingly increasingly) do not correspond to popular vote percentages.
Third, polls are snapshots on how people feel on a certain day. Americans seem to be particularly fickle in their opinions recently, perhaps due to the economic turmoil, so don't trust that today's lead won't disappear tomorrow.
Finally, many polls do not remove unlikely voters (though you do see some figures concerning "likely voters"). Polls of people who do not vote are fairly useless, but pollster's haven't been very successful in predicting who will actually vote. Thus, the tendency is to include respondents who are registered and say they plan to vote, without looking at their demographics to see what they've done in the past.
For all these reasons, if you're an Obama supporter, you should be worried and if you're a McCain supporter, you should have some hope. Either way, vote!