One problem with my eeepc now, is that I didn't get the battery life it claim, on windows and linux on the eee pc. That is 8 hours. Currently it is only 4.5 hours.
One way to figure out what is using the power is, using powertop. It is a open source tools to use to display the process that is using the power, and give recommendation. Which is cool, because, it actually very convenient. But of course, you really need to do it manually, because the solution is missing after a reboot.
For ubuntu user, just
sudo apt-get install powertopAnd powertop need to be run by root.