I upgraded to the new Feisty kernel, 20-14, and lo and behold, my accelerometer readout started working. I can now run hdaps-pivot to get values as well as hdaps-gl to see a rotating GL rendring of my laptop.
That's cool. Wait, no it's not.
It turns out, although now it can read out values from the accelerometer, that's all it does. To get actual hard disk protection, you need a userspace daemon, and a kernel patch. Which leads you to this page.
To paraphrase, the patch is out there, it's for an older kernel, and it's too intrusive for Ubuntu guys to feel comfortable including it.
Fantastic.
I guess the old bit of wisdom is still true: if you really want to use Linux, you'd better be ready to compile anything yourself.
Maybe someday I'll get around to patching my kernel. I found out about apt-build, which looks like it might make the process of doing so just a tiny bit less painful.