Eric Lawrence, John Sides, and Henry Farrell have put out a new study:
We examine deliberation, polarization, and political participation among blog readers.We find that blog readers gravitate toward blogs that accord with their political beliefs. Few read blogs on both the left and right of the ideological spectrum. Furthermore, those who read left-wing blogs and those who read right-wing blogs are ideologically far apart. Blog readers are more polarized than either non-blog-readers or consumers of various television news programs, and roughly as polarized as US senators.