It shouldn't make a difference for most people. The biggest issue with readability is contrast, so whether you have black-on-white or white-on-black, you're good.
Some people say dark text on a light background is easier to read, which might have something to do with the fact that books have worked that way for hundreds of years.
However, then there's the issue of light backgrounds being hard on the eyes. I don't know about you, but when I open a new tab with all the lights off, I'm immediately blinded by a white screen. This isn't an issue with books because they don't have backlights.
The contrast is high enough either way. It's more about image, honestly. Dark backgrounds can look less professional and more 'edgy'. Lighter backgrounds represent professionalism, openness, and positivity. That's why most sites that represent a cause or organization have a light background with dark text. This includes websites about 'going green', which is ironic considering a site with a black background would use less energy.