Opinion Polls

[aap1966]

This post is not intended to be partisan, (I'm trying to learn, not preach) so here goes.....

I was wondering how much weighting has to be applied to opinion polls to get an accurate picture of voting intentions.
Let me explain, Thatcher always did better in the elections than polls predicted, the explanation being that people felt hesitant to admit their intention to vote for her to the nice young pollster at their door, or on the phone, but in the privacy of the voting booth were quite prepared to do so.
In Australia large portions of the media are pushing the line that the only possible explanation for not voting Obama is racism.

So, 2 questions:
1) Is a similar line is being pushed in the U.S.?
2) If so, is it possible that people who have no intention of voting for Obama are apparently supporting him in polling, but will vote McCain on the day?

BTW, Good luck to any "Pelicans" staring down the path of Gustav--we're thinking of you guys.