I found out about this bug from Digg this morning. After investigating, I found that the load cycle on my harddrive was increasing rapidly, both on AC and on battery. This sounds like a fairly serious bug, and should be dealt with quickly. I've made the following changes, which seems to have fixed it (load cycle doesn't increase on AC, and doesn't seem to increase much on DC).
Changed "$HDPARM -B 1 /dev/$drive 2>/dev/null" to "$HDPARM -B 254 /dev/$drive 2>/dev/null"
$ sudo on_ac_power; echo $?
$ sudo ps axu | grep apm | grep -v grep