I think comments are once again enabled. There were lots of problems with spammers and I tried to use the TypeKey service but apparently set it up incorrectly. It's working correctly now, so you can comment after creating a free TypeKey account (also useful for commenting on other sites).

Now, for anyone having a problem with TypeKey on their Movable Type site and getting an error message like this: "The site you're trying to comment on has not signed up for this feature," here's the secret: in addition to adding the TypeKey token to your Movable Type settings, you also have to add the path to your comment's script to your TypeKey account. You need something like this: "http://[your site]/mt/mt-comments.cgi"