I've heard from a few fellow Democrats who seem to feel that Obama is a far better and more inspiring candidate than McCain and can't understand why Obama isn't 10-20 points ahead. A little perspective: presidential elections are rarely won by such large margins. Twenty points is considered a landslide. The only candidates who've gotten into that range in modern times are Lyndon Johnson (1964) and Ronald Reagan (1984), both of whom were popular incumbents running for reelection during economic booms.
Clinton beat Dole by less than nine points. Bush beat Dukakis by about the same margin. Clinton only beat Bush by about five. And 2000 and 2004 were nailbiters. In fact, the last non-incumbent candidate to win by more than ten points was Dwight Eisenhower in 1952.
The forecast I posted earlier is pretty consistent with recent polling, showing Obama winning by around four or five points.
Late update: See here. I would also add that, with the economic indicator I'm using, the economy is doing about as well as it was in 2004. Not stellar, but not a recession, either.