I don't have much to add to her eloquence, but I'd like to say that my personal realization that the Democratic Party (now known, apparently, as Obama for America) no longer cared about Democratic principles was when I read the "Bowers Manifesto" - a statement of "principles" written by Chris Bowers of MyDD. It was a proud admission that the the working class was no longer invited into the Democrats' Big Tent. It upset me so much that I wrote two posts about it: here and here.
That's where I'm coming from. We all become PUMAs in different ways.
It would be nice if the Obamans and the Party Leadership could respect and recognize that we have real grievances, rather than dismissing or insulting us. But then, if Obama and the Party Leadership had empathy and respect for their constituents, they wouldn't be who they are.
And I'd be happily pulling the lever for Obama in November.