Britt Peterson compiles the evidence:
[A] number of new studies suggest that, in certain key ways, people with that much money are not like the rest of us at all. As a mounting body of research is showing, wealth can actually change how we think and behave—and not for the better. Rich people have a harder time connecting with others, showing less empathy to the extent of dehumanizing those who are different from them. They are less charitable and generous. They are less likely to help someone in trouble. And they are more likely to defend an unfair status quo. If you think you’d behave differently in their place, meanwhile, you’re probably wrong: These aren’t just inherited traits, but developed ones. Money, in other words, changes who you are.
Paul Waldman thinks the political implications are pretty limited:
[E]ven those who come from humble beginnings have left those beginnings far behind once they get to a position to run for president. Even if they haven't made millions, they've been in a position of power, where all day people cater to their needs and speak to them with deference. Some people are changed more by this than others, and the greater likelihood that a rich, powerful person is a jerk can't tell you whether a particular rich, powerful person is actually a jerk. So the best predictor of what a candidate will do once he or she is elected isn't the judgment you can make of what lies in their heart, or the circumstances of their youth. It's the things they say they're go to do.
The Dish 