Digital Pathology Blog contemplates his liability needs as a blogger. I would encourage this given my experience, particularly if "whistle-blowing" or ranting occurs on your blog. Some offerings for bloggers insurance are mentioned here. I'm still shopping options and readers will likely see advertising creep in to my blog to offset expenses.
I'd also encourage all bloggers to understand the legal definitions of defamation, slander, and libel.
My Problem: "Bloggers Beware"
Where I try to decide if I should continue blogging: "So Now What?"
From the Daily News / Opinions: "Bloggers Must Learn A New World Order to Win Fans, Respect"
Electronic Frontier Foundation Cyberslapp Website.