[Erasmus]

Glowing letters instead of a glowing screen would be good in places where you don't want a blaze of light. It would lengthen battery life, too.

Not with any backlit technology, unfortunately. Quite possibly, however, with OLEDs, which are coming.

[HiTech RedNeck]

Why backlighting can’t be made to dim (and save power) in a “dark room” mode, is not an engineering issue, only a design issue. And any pixel addressable screen could go to negative video.