There's not much more to say. It used to work and stopped about a week ago. I'm running on Debian using nginx, spawn-fcgi, and memcached.
I even did a fresh install of WP 3.0.1 and it didn't work, from which I infer that there's some interaction with my system, but the machine is pretty minimal, since it's only being used for WordPress. I'm also pretty frazzled at this point, so I certainly could have made a mistake in my fresh install.
Has this ever happened to anyone else? Googling was pretty hopeless (too much stuff from old version of WP), so I'm turning to here.