Andrew Gelman's research (pdf) finds that both left and right worry about polarization but "we can’t always agree on what exactly we’re polarized about":

On the left are concerns about economic polarization, the widening divide between the haves and the have-nots and the increasingly unequal distribution at the high end, with the richest one-tenth of 1 percent of Americans taking 7 percent of the income, which is associated with the declining influence of labor unions and a political tilt toward the rich. From the right come concerns about social polarization, Red America versus Blue America, a clash of values so strong that liberals can no longer talk to conservatives, a country in which ordinary people struggle with a liberal media and a decadent cultural elite (“Hollywood versus America,” in the words of movie critic Michael Medved).