Well, that happened sooner than I expected. I've switched from WordPress to Habari, and so far, I like what I see.
The default template is rather crufty, and it uses a loose DOCTYPE, but I was going to give this place a makeover anyway, so no big issue there. The PHP code looks considerably healthier than that in WordPress, and the use of PDO for database connectivity is reassuring, as the prepared statements and bound parameters should guard well against SQL injection attacks.
I had a slight issue when importing my WordPress data, because my WordPress user and Habari user both had the same name. Simply changing one or other username solved the problem, allowing me to import all posts, comments, and pages, and I was then able to delete the default Habari user, and make the imported WordPress user (and all of the associated posts) my primary account.
The spam detection is pretty good, even with using something like Akismet, and has only missed one so far - it had no links in it, and looked innocuous enough at a glance. Comment moderation is turned on by default, though, so that caught it. I'd like to see some way to set the options for the included spam plugin without having to edit the PHP file, and I hope that Habari introduces comprehensive options regarding commenting in a future release, such as auto-approving subsequent comments from approved posters (Habari might already do this, I don't know). There essentially are no options regarding comments at present, beyond a per-entry "Comments: yes/no?" choice. I also need to look at how it parses the comment body, and what markup it (doesn't) allow.
It's still rough around the edges, but the whole architecture of Habari feels more friendly than that of WordPress - I'm looking forward to further improvements from the Habari team in future.
Apologies in advance for any issues due to the switch - leave a comment on this entry if something doesn't work as expected, and I'll try to fix it.