I ask myself this question from time to time. But in the end I come to the same conclusion as Daniel Lemire:
„if blogging prevents you from getting tenure, something is very wrong with your blogging or your school.“ [see The negative myths about academic blogging]
On the contrary, being open about what I think hopefully gives me some competitive edge. And, again following Daniel’s argumentation, I doubt my colleagues will pay any attention to my blog when I apply for a professorship. Do you?