After a bit of googling about, it seems that I'm affected by
Ubuntu Bug #111375, which itself seems to be
kernel bug #8423. According to kernel.org's bugzilla, this has been fixed, but a new Ubuntu kernel hasn't been compiled yet.
This puts me in a bit of a bind. I could, conceivably, apply the kernel patch myself--but then that would leave me up a creek with the nvidia drivers. Or I could just wait until the patched kernel shows up in the repos, and just live with the fact that I don't get speed-stepping. I'm opting for the latter. That way, I could probably just run a 32-bit kernel and not have to worry about the various workarounds for flash and java.
So, while I'm waiting--c'mon Ubuntu team!--here's some entertainment:
Click to view