A very interesting topic.
I suppose if you are writing in your capacity as a professor, you really shouldn't be anon.
However, if you're "on your own time"...
I have reasons to remain (mostly) anonymous, which don't really involve my career advancement as much as privacy issues, but it's something I struggle with.
I am admittedly quite paranoid but on occasion I even protect my pseudonym with a pseudonym. Why is that? Well two reasons really. The first is that there is plenty of evidence of implicit bias against women in science and it is more comfortable for me to know that people reading what I have to say are not subconsciously judging/dismissing what I say on the basis of my gender, so on occasions such as now when it is relevant to admit that my gender is female, I dont do it with my main pseudonym as that would wreck the effort I am trying to make to ensure that that speaker is on the masculine side of gender neutral. Secondly, I have a bitter and twisted history having been harassed out of my previous employment. I wanted to take legal action but in the end I couldnt afford it (that's one of the problems with being unemployed... And in the country I was employed in you cant find lawyers who will charge only as a proportion of any settlement they may win), and friends also finally convinced me that this could waste years of my life for very little gain. Growing up believing that "truth will out" and in "truth, justice and etc etc" and only learning in your late 30s (I was completely naive and a very slow learner) that this is a bunch of crap can tend to make one a bit bitter. However I dont want this experience to define me for the rest of my life and I dont believe it has to. I believe that I can contribute to the debate and let my past experience inform but not dominate my views. What I do think though is given the topics I choose to write on, my words are likely to have zero credibility if they are seen as the rantings of a bitter twisted ex-female scientist and egotistically, I do hope that I have some useful things to say. I too struggle with anonymity: part of the reason that I was harassed out of my previous employment is that I was not afraid to openly say what I think and to challenge unethical behavior directly. So I set a rule such that as long as I write things in such a way that not even my partner could identify who the author is, then I can allow myself to remain anonymous. This also helps (I hope) to minimize the bitter tone as well.
I've been known to say that policy makes a poor substitute for sound judgment. To me the comments here and the explanations of the anonymous Chronicle authors reflect careful consideration of individual real-life concerns.
The other article struck me as very limited in its concepts of real-life consequences. I found it interesting that the real name advocate is described as a former academic and current art critic. Those two bits of information, attached to that particular essay, tell me far more than the author's real name.
I write anonymously online, for reasons that are important to me, personally. I'm also very, very conscious that the credibility of my online persona comes only from consistency of my online verbal behaviors. As a result, I'm much more careful about my choices of words in online writing than my everyday speech. (To the occasional detriment of my everyday life. Ouch!)
Female Science Professor has blogged on the Chronicle articles, too; read what she has to say at http://science-professor.blogspot.com/2008/04/my-two-anonymous-cents.ht…