I'd better get in here now, because I know most will disagree with this.
Many white people I know also think that race is behind the rhetoric. I certainly think it contributes to it. So much of what you hear has a 'he's not one of us' subtext--see the birth certificate flap (many who use this don't see its racist origins) or Gingrich's Kenyan tribesman comment. While that's part of it, I think there's more.
The right has moved further and further to the right over the last few decades, and now many, with their views constantly reinforced by a special brand of media that's sprung up, see themselves as the center, and this distorts the whole spectrum. Policies that are similar to ones actually supported by Reagan now become socialism. Everything center-left (and some moderate right) becomes a threat to our way of life.
And Obama personifies that threat. Muslim name. Not the type of guy we usually elect. Again, there's a racial subtext, but, perhaps more importantly, there's a fear of change, a fear of losing hold on the country and its traditions. You would have seen the same kind of attacks, if not worse, had Hillary been elected president, I think.
Now, having said that, I'll leave the discussion to those who will tell you Obama's a radical liberal socialist commie Nazi.
btw, I'm disappointed with him because he has continued too many of Bush's policies, particularly regarding government secrecy and mining private data, his health bill was weak, and he hasn't rallied the American people behind him. Unlike many here, however, I want him to succeed.