Dr. Crazy and Profgrrrl have responded beautifully and at length (and with much less snark) on their blogs, Dr. Crazy addressing the pseudonymity versus anonymity issue and Profgrrrl explaining patiently why someone might not want to have blog posts be the first thing you see when you Google someone's name.
I admire the people who post under their own names, like Kathleen Fitzpatrick and Miriam Burstein, Claire Potter, Amardeep Singh, and Michael Berube, but I don't want to do it--and, to judge from the far more articulate blogposts about this, others don't, either. Why?
In short, your blogging identity, as opposed to your scholarly identity, is more or less in your control. In real life, whether something is published or not, what people think of your scholarship, and so on are all outside your control. In blogworld, your identity depends on how you present yourself: honest, irreverent, angry (like the Angry Professor), or whatever else you choose to be. Plagens might say that this is inherently dishonest, because you're not using your real name, but then, does blogworld have to answer to the demands of the real world, or just to report its absurdities? I'd say the latter.