(The day after my untimely wrecking of a perfectly fine OS X setup, that is.)
Charles thoughtfully added that I could just have trashed the LoginWindow preference plist. D’oh is the correct expression to use here - I do nothing if not fool around with plists all day.
My other users on this computer apparently hit permission hell - the user and group numbers didn’t match up with the old ones after all, and I had to change the owner and group owner of some home directories.
However, this whole exercise wasn’t a complete failure after all. A problem that has persisted since nary two months after installing OS X 10.4 has been wiped off the face of the earth - the very neat System Preferences search field works again. (Before, after being wrecked, it wouldn’t even show entries matching the name of the preference pane, and I cleaned out caches, search indexes and, yes, even the preference plist, and it didn’t work, not even on a new user. Now it works. Go figure.)