An interesting post at All Spin Zone argues that the Democratic infight has polarized the blogosphere and impacted traffic. The warfare is open, with a "strike" by Hillary backers at Kos.
Anecdotally, I'll buy it; MyDD is clearly in the Hillary camp and Kos is fired up and ready to go for Obama. But my own experience is that traffic waxes and wanes with the election cycle, and the drop in traffic coincides with the slowed-down pace of primaries.
Interestingly, if you buy the premise, it looks like the Hillary folks don't want to hear their candidate critiqued: traffic on the pro-Obama sites has dropped more, while traffic on the Clintonista sites is flatter.
As for me, it's hard to measure; being Iowa-based, my traffic peaked at caucus time, and I had a huge artificial spike last week from a Bob Dylan fan site linking to my commentary on the murders. Busiest day ever, but can't feel good about it.