I've read e-books on a Palm III, a Handspring Visor (PalmOS), a Nokia N770 and N810 (Maemo), and various Windows boxes. I do not off-hand recall a time when the fact that all the non-PC devices were backlit would have made a difference in me reading vs. not reading.

The Kindle 3 with the cover Amazon pushes looks like a really nice solution, if you're a person who would use it.