After the recent messages about comment spam, I have upgraded both Movable Type and MT-Blacklist. Not that my comment spam problem became bigger, since my setup is different enough from the regular MT site to stop them. I have renamed my comment script and, more important, I force commenters to preview. This alone blocks all spam coming in through the comments.
The problem is that once in a while I receive spam through the trackback interface. Since trackbacks, comments on my writings left on other sites, are always generated automatically, I have no way to force a preview and have to use the default workflow. As a result, once in a while a spammer gets through and manages to place many spam on my site before I have the time to add his URL to the blacklist. Of course, after that all spam is deleted with a single click.
Conclusion: So far I am still winning the spam war, but only because I am on top of it with upgrades and by quickly removing spam.