I use a black background for everything. It is the most efficient color (or non-color) for your monitor to display. It is also the most energy-efficient, as a monitor displaying all white can use up to twice as much power as one displaying all black. It's much easier on the eyes as well. I get a headache looking at a mostly-white screen all day.

I hate how some Seattle-based software companies try to make applications work like paper. Paper is paper; a monitor is not. Most monitors only display a max resolution of 72 DPI, while paper is capable of 600 DPI and higher... They are not the same, so why try to make them the same. This is an example of a bad metaphor.

White text on a black background also has better contrast. If there is any color bleeding from the light of the activated phosphors, it bleeds into the black surrounding the text, perhaps making the text slightly bolder. If you have black text on a white background, the white bleeds into your text, making it thinner and harder to read.

I have also configured Internet Explorer to force all web pages to a black background. Of course this causes a problem for sites who specify black text explicitly, unless you also tell IE to "Ignore colors specified on Web pages" under the Accessibilty button in the Internet Control Panel. The default link colors also suck with a black background, so I have lightened each of them up to a luminance value of 200 from their defaults (under the Colors button in the same control panel).

Everything (including Everything) looks awesome this way. It's nice to still have some control over how I want stuff presented to me, rather than large consultant-committee-driven corporations telling me how I should live my life.