In case anyone else is having issues with the same thing:
Even since the gcc4 update (which pulled in kernel 2.6.13), ACPI has been a tad wonky.
Certain nodes in /proc/acpi (and outputs from `acpi`) either disappear or remain static. For a few days now, my (plugged in) laptop has been at "Battery: 35%, discharging" and my thermal zone is missing.
It seems I can get sporadic error messages, but nothing worth reporting. Others have also reported the issue on IRC.
In addition, the newest ndiswrapper (1.4) hangs for me when it attempts to set up wireless power management modes. I have a feeling this is related to the acpi issue, so I am hoping to get this fixed before messing with ndiswrapper again.
As a note, the current PKGBUILD uses lenb's acpi-20050815 patch, yet he has released acpi-20050902. I have no idea if this will fix it or not (I doubt it, but it's worth a shot).
If anyone has more information, please provide what you can.