In the discussion on Managing your brand as a Librarian, one of my points is that you are what you say in any public forum (conferences, blogs, comments on blogs, Facebook, Twitter, meetings, etc). Fortunately or unfortunately that all intersects into an image. For new librarians or even experienced librarians looking to change jobs, understanding this whole package will be as essential as your resume. You are making a huge mistake if you don't think that this matters.
I have been a subscriber to more than a dozen library oriented listservs for over 10 years and without fail, someone commits professional suicide at least once a year. Someone will complain about outrageous work or school assignment, mean professors/directors, crazy patrons/students, policies and procedures, politics, religion, race, gender, etc. in a public list forum. (I am ashamed to admit I am still subscribed to some of these lists just so I can watch the train wreck that will eventually show up.) It really doesn't matter if they have a "case" or are speaking up on a real issue, what comes across is usually outrage/anger and then deteriorates into name calling and a flame war.
The only thing you will achieve is a brand or label as a complainer. When I mention this, invariably someone will say they have a right to say what they want and that they feel strongly about the "issues". You are right. You do have the right. However, those looking for help are thinking: "Oh great, that person is going to require a lot of work and never be happy." Public service is thankless and difficult. If you are going to fold over a cruddy teacher or complain about the crazy patrons, my feeling is you won't make it with the public or you will be so unpleasant, no one will want to work with you. Intelligent discussions of problems require us to be thoughtful and professional. This means not responding in anger and certainly not posting it for everyone to see.
The take away from this discussion is whatever you put out there on lists, blogs or any forum will be what the people hear. If all they hear is complaining, then that will be your brand. Want to really change something? Work hard, do your job and write down what you think and reflect. Implement change where and when you can and let your "brand" speak for itself. Whining from the cheap seats helps no one and changes nothing.