An excellent statistical guide to the election's ongoing state-of-play is the website 'fivethirtyeight.com' - http://www.fivethirtyeight.com/ According to its latest calculation, the probability of an Obama victory is 94.7%, compared to just 5.3% for McCain.
There's an important qualification to make here, though: the percentages above are equivalent to predicting what would happen were there 1,000 elections held simultaneously on Election Day - Obama would win around 947 of them, and McCain just 53. But here's the thing: there aren't going to be a thousand elections on November 4th, just one. McCain's hope will be that one of those 53 possible combinations comes up for him on the day.
For Obama supporters then, the key will be voter turnout - ensuring that the swing states that are leaning his way at present go for him on election day, when the polls really count.