CPU Frequency scaling
When I got my new laptop (an HP Pavilion DV6262 if you are interested, and yes I am happy with it so far) it took me a while to get Ubuntu fully working on it and so for a short while I was using Windows Vista. When I got Ubuntu working it appeared that battery life was significantly shorter than under Windows Vista and although I now attribute that to the gnome power monitor being more pessimistic than that of Windows (and having a few bugs, like the most erratic estimation of remaining time I have ever seen) at the time I was looking for ways to stretch the battery life when running Linux.
A quick bit of research suggested I should try CPU frequency scaling which slows the CPU down when demand on it’s resources are lowered. This was relatively easy and didn’t appear to affect the functioning of the system much. I didn’t conduct any test and just took it for read that I was saving energy. A few weeks later and I was discussing strategies for saving energy in data centres since that is now becoming a large factor in the running costs, and hit upon the idea of using CPU frequency scaling to reduce the thirst for energy a densely populated rack has. This sat at the back of my mind for a while but never got much further.