relief and disappointment
I just spent an hour preparing a bug report on ALSA. It was giving strange permission errors if I wasn't root, even though I could play sound as normal users using OSS or writing directly to the sound device. Neither of those are good because only one sound can be playing at a time (when you try to play more you get "/dev/dsp: Device or resource busy").
Then for a second-to-last test (last was going to be dusting my mobo because my soundcard is onboard), I rebooted into a newer kernel (uptime was probably around 25 days, I forgot to check before rebooting) and it was gone.
From all this I learned:
1. Reboot in the face of bizarre errors if you've tried everything you can think of.
2. ALSA has no connection to /dev/dsp. The permissions of /dev/dsp can be 600 with the owner as root and the group as root, but ALSA will still work fine as a normal user.
3. I need a new soundcard. Mine only outputs to the left speaker unless I fiddle with the way the jack cable from the speakers is plugged in (on either side) to the point where both speakers play sound, but it's crackly and the jack falls out of place easily. I tried plugging the same speakers with the same jack cable into marvin (my server) and playing something, and it worked fine.