Someone pointed out that it was impossible to leave comments on this blog (and registration was disabled).
I was worried about “comment spam” when I first created the blog, so had it locked-down. I’ve now enabled comments for registered users (and enabled registration). The first two comments for a user must be approved by me.
EDIT: well, that didn’t take long – I got a bunch of robo-registrations. I’ve installed the “zero spam” WordPress plugin – let’s see if that helps!