I like dark on light; it's literally easier for me to read (though there is a medical cause for my choice).<p>I have Keratoconus, so there are very few corrective lenses which can actually help me have good clear vision. Light screens with black text cause my pupils to contract, which results in better focus (it's related to the reason that pinhole cameras work without any lenses).<p>If I do light on dark (my favorite colorscheme was Zenburn), the text gets too fuzzy to read at anything smaller than 14 point. On the other hand, if I use dark on light (I prefer bclear now) I can read text comfortably at 8 point.<p>It's certainly painful on the eyes if the rest of the environment is dark, but if you have a reasonably well lit room, I've noticed very little eye strain.<p>While my experience obviously does not carry over well to the population at general, it could help explain why dark on light is easier to read - it's easier to make out the details.