I can't believe that people would actually hire attorneys because of posts on DC Urbanmom. I would assume that most of these people are from daycares (due to bloggers stating they are no good, etc.)?
I found this on the net which I think is a really good overview:
https://www.eff.org/issues/bloggers/legal/liability/defamation
With defamation type of lawsuits, truth is usually an affirmative defense. But if something is absolutely UNTRUE, you may be liable for allowing the republishing to continue. This may be hard to decipher when the sources are anonymous.