How to enable laptop-mode?

The steps listed in the question are correct, the only thing remaining is to reboot your machine (possibly a couple of times). After that laptop mode will be enabled:

~$ cat /proc/sys/vm/laptop_mode 
2

Once laptop-mode is working, you can follow these steps to configure laptop-mode...

Edit /etc/laptop-mode/laptop-mode.conf and change

ENABLE_LAPTOP_MODE_ON_AC=0

to

ENABLE_LAPTOP_MODE_ON_AC=1

Also check for the battery mode on battery state and turn it on if it is off by changing the value to 1

e.g.: ENABLE_LAPTOP_MODE_ON_BATTERY = 1

You can set many other option in this config file (the file has many self-explanatory comments). You should try setting them to your liking.

When you're done, restart laptop-mode with:

sudo /etc/init.d/laptop-mode restart

P.S. If laptop-mode is still not on after rebooting the machine, you can try playing with this command as well to manually enable it:

Check that it's active on AC with for example:

$ sudo laptop_mode start

which should output:

Laptop mode 
enabled, 
active [unchanged]

Hope this helps..

enter root by

sudo su

and then

echo 5 > /proc/sys/vm/laptop_mode

If you want more tips to save power check out LessWatts. I was able to extend my battery life from 2 hours to 3 and a half.