As they say over at the Guardian, Comments are Free. Of course, since it's The Guardian, you'd be gullible to take them at their word without some fact-checking, and so, true to Guardian form, at second glance it turns out that comments are perhaps free, but first you have to register. Since I haven't, I can't say what this might entail. (Something to do some rainy day).
In the meantime, however, Silke sent me a cheerful e-mail, because my comments were configured so that you had to be registered at Google to leave any here. So I've reconfigured (I hope), and now comments really are for free. Ahoi, all you multitudes of loyal readers who aren't registered at Google: even you can now leave messages, freely and for free!