Update: Comments seems to be working normally again. For now.
In their never ending quest to make blogging harder, the people at TypePad installed some sort of comment filter today. So far, it has captured lots of comments, none of which has been spam. It's taken me much, much longer to approve the comments captured by the new spam filter than it ever took to remove actual spam that got through before. Thanks, TypePad.
So, if your comment does not appear immediately, the spam filter probably grabbed it (it seems to block comments somewhat randomly - some have been blocked for no good reason that I can detect). I will approve the comment as soon as I can. I will also turn the filter off if I can figure out how, but so far I haven't been able to find a way to do that.