I had temporarily disabled comments earlier, but now commenting is back on.
The difference is that now you must be registered with a username and password to leave comments. This will hopefully cut down on the amount of spam and abuse that has littered the site’s pages recently.
Simply register as a new user. Once logged in you can change your account settings and set how you’d like your name to appear in the comments. You’ll only have to do it once!
Update: It should be mentioned that if you’ve already registered a username for the discussion forum, you’ll need to register a second account for commenting on the blog posts. Unfortunately, the two systems are different pieces of software and can’t use the same set of users. But feel free to use the same username and password for both if it makes it any less confusing! (Thanks, Elwood!)