Bloggers who are job hunting and use their blog as part of their portfolio shouldn't post on their personal blogs while at work. The message it says to those potential employers is, “I could really care less about your workload. My blog is more important.”
Now there's really nothing wrong with the spirit behind this, because I hope your life comes before your work. Work is what you do at the moment to allow you the funding to do what you want with the rest of your time.
But think before posting. Think about the message you are sending.
That said, I'm on Day 5 of a new job, and I'm at my desk writing this. Think about the message I'm sending. Or think about something else. Just think once and awhile. But don't hurt yourself doing it.