Information Wants To Be Free has posted about Safe blogging, meaning blogging that is work safe and work friendly. As someone who has only blogged through my own workplace, I don't see a problem. Yes, you cannot complain about customers and coworkers in your blog, but you can comment on larger issues and speak in generalities. Yes, I have to watch my language because I am actually officially blogging on my library's site. Yes, I am careful, but I hope that I still offer perspectives and commentary that are insightful and timely.
Both of my blogs lean more toward the professional posting than the personal. I write as a professional on professional topics. I take professional stands and make professional comments. I have never regretted posting anything here, but that is probably because I am careful and filter my thoughts first. But really, if you are going to be posting as a librarian, then you really should be being careful. It only makes sense to avoid slandering co-workers and patrons.
So your blog may change along with your new job, but that should be expected anyway. Your perspective is going to adjust now that you are viewing the world through a specific library lens. And hopefully now that things are less theoretical and more actual, that change will be a very positive one.