Comment 3 for bug 239419

Hmm. That's strange. I've just reinstalled ubuntu, added these lines:

if [ -f "/etc/default/acpi-support" ] ; then
 . /etc/default/acpi-support
 if [ x$ENABLE_LAPTOP_MODE = xtrue ] ; then
  echo "Laptop mode enabled, laptop-tools has nothing to do"
  exit 0
 fi
fi

and it worked for me (cat /proc/sys/vm/laptop_mode shows 2).

Are you sure you have ENABLE_LAPTOP_MODE=true in /etc/default/acpi-support?

Also don't forget to replace original laptop_mode_enable and laptop_mode_disable in /etc/acpi/power.sh with this:

function laptop_mode_enable {
    $LAPTOP_MODE auto
}

function laptop_mode_disable {
    $LAPTOP_MODE auto
}

The original is disabling laptop-mode in 5 seconds after you plug in to AC. :-/