I was searching for a clean way to disable standby today in Windows XP and bumped into an interesting
Powerpoint presentation on the ACPI subsystem in Windows XP.
One of the more interesting tidbits mentioned was a 'tweak' that was added to service pack 2, that is disabled by default, which makes the ACPI subsystem a little bit more responsive when you have many devices on sharing the same interrupt as the ACPI interrupt, which I've seen happen on "crowded" systems.
If you want to enable this, do a bitwise OR of 0x00000100 at HKLM\System\CurrentControlSet\Services\ACPI\Parameters\Attributes
Most systems I've seen do not have a DWORD Attributes key, so you might have to create it.
If you have to create the key, just enter in 0x00000100 for the value since there isn't a pre-existing value to OR.
In Vista and Longhorn, this enhancement is enabled by default, so if you are already running under Vista or Longhorn, no need to apply this.
You can also read up on the massive changes the ACPI subsystem went through in Vista
here.
One of the more noteworthy items in that PowerPoint, at least from an end-user perspective, is "native" screen brightness controls for laptops, as long as they have proper ACPI support. Anything that reduces the amount of programs needed to support laptop controls is a good thing in my book. I typically try to run the least amount of OEM cruft I can get away with.