2) I bet if u do an experiment, u will find that looking at darker blackgrounds for a longer period of time is far less tiring on the eyes.
Some people find it hard to read [on dark backgrounds] because of the contrast. Well, these people already have bad eyesight to begin with; Astigmatism. Get a good pair of glasses my friend. These people are also the same ones who can't see lights well at night.
But we can all cater to such people using less contrast, i.e; Grey on Black instead of white on Black. I used Dark Green, which I think is even better.
3)Last of all. Black Save Electricity! Do you know Google will save like 183849u4333watts of Electricity if it uses a black background? If you don't believe, GOOGLE it :D.