The WordPress installation was hacked with some sort of embedded redirect to “tigoe.net”. No idea why anyone would want to waste their time with that, but whatever.
Didn’t see any easy way to fix it (nothing in the .htaccess file), so that installation was deleted and we now have a brand new one with all of the old functionality (and almost none of the content!). Looks like that Mayan prediction of a new beginning was surprisingly accurate.
UPDATE: I’ve recently discovered that the site ended up wiped that first time due to Dreamhost’s server move. Turns out that someone had the same database name as I did, and when everything was consolidated onto the same server my database information got overwritten by that other blog’s. I’m using a more specialized name now, so hopefully such a thing won’t occur again.