If laptop mode tools service won’t start and you’re running a 3.1.x kernel, just add the kernel version in /usr/sbin/laptop_mode line ~ 500, so it should look:
case "$KLEVEL" in
"2.4" ) ;;
"2.6" ) ;;
"3.0" ) ;;
"3.1" ) ;;
Don’t forget to check the file after every updates.
Source: Gentoo Forums