From Nate Silver at fivethirtyeight.com:
I have written for perhaps a dozen major publications over the span of my career, and the one with the most thorough fact-checking process is by some margin Sports Illustrated. Although this is an indication of the respect with which SI accords its brand, it does not speak so well of the mainstream political media that you are more likely to see an unverified claim repeated on the evening news than you are to see in the pages of your favorite sports periodical.
One of the questions triggered by the Frontline program [on Lee Atwater] is what would have happened if Atwater were still alive today; might he have had more success in undermining Barack Obama than Steve Schmidt apparently did? My answer is very probably not, because the blogosphere serves as the fact-checkers that the mainstream media is too negligent to employ.