Dark themes = Longer battery life

The backlight on any given laptop is it's most power-hungry component.

if your screen is shiny and white, it will eat through the battery faster, and generate a modicum of extra heat.

If only the majority of dark themes that are available for the main desktop environments didn't suck. The theme developed for Crunchbang Linux is an exception to that rule, but it's one of only a few.

Of course, most economical of all, the Command Line Interface uses less power than any dark theme, but that way madness lies...