The server that hosts this blog has had an awful lot of spam attacks recently, and when I call them attacks I mean it. The people doing this know full well that the spam isn't getting accepted. It's purely malicious, and it's designed to shut down the server. This has been a long-standing problem, but it hasn't usually been so concentrated in its intensity. In some cases, I think it's motivated by spite, simply because they can't get their spam through due to the pretty effective means of preventing spam in the new version of Movable Type. In others, it might be politically motivated. I have no idea if the latest attacks have been from one person or many, but in any case it's been shutting down any operation that requires making changes to the way the blog appears, including comments. It requires someone noticing and contacting the right people and then waiting for them to kill the process that's hanging up, and sometimes that takes a while, particularly if it happens at night.
So if you find that you can't leave a comment, that's why. Please be patient. Rest assured that I'm far more frustrated by this than you are. If you'd like to leave a comment and can't, I'd appreciate you writing the comment and saving it somewhere and then submitting it later at a time when the server isn't hung up, rather than not submitting it at all. If you have a blog, you can always respond to something with a post of your own (especially if you'd like to let me know about it, and I can continue the discussion there), but I'd actually prefer in general that you continue the conversation on the post in question when the comments are working, even if that takes waiting a bit sometimes.
Update: I believe the spamming issue has been resolved now, but there's a different problem. Many of my old posts have been renamed for the new format but still exist with the old format and don't allow comments. I'm trying to figure out what I can do about this. For now, if you end up on any page that shows the old format, and you'd like to leave a comment, just replace any underscores with hyphens, and it should show it with the new format and allow you to leave a comment.
Update 2: I think the renaming problem is resolved now. If you discover anything funny about posts not showing up, showing up with the old template, or something like that, please let me know.