As you may know there have been some very high profile bloggers who have lost their jobs as a result of their blogs. Mark Jen was fired from Google after blogging about life at the company, and a Delta Air Lines flight attendant was fired after posting photos of herself in uniform on her blog. While I don't know of any librarians who have been fired specifically for blogging, Cheryl LaGuardia and Ed Tallent in Interviewing: Beware Blogging Blunders writes how your public blog can hurt you in job interviews.

Blogger's rights is a controversial topic. We are not journalists so we are not afforded the same professional protection as they are. Clare Leibfarth forwarded a link to me, EFF: Legal Guide for Bloggers. It is a "basic roadmap" to the legal issues you may confront as a blogger.