It's worth noting that light text on black was very popular a decade or so ago (like when ENworld started), but that the majority of sites with a large amount of text have moved to dark text on a light background because it has greater legibility, especially on modern monitors and at smaller type sizes.
For those people who have said 'argh my eyes', I have to wonder where you go on the internet nowadays!
Also, as Umbran said, a black background isn't exactly the kind of thing which you are likely to be reading at work, so the stealth/disguise aspect is important for some people.
For people for whom the whole thing is too light, a scheme that put a darker colour or background behind all the threads would probably be more appealing. At one point in the past we had a 'PHB' theme, which was very much pale yellow and light brown and was quite appealing.
Cheers