My Macbook works by ambient light and can be turned off.Meh... For computer keyboards, it can be a useful situation under very limited circumstances. For anything that's powered by batteries (like a TV remote), it better have an automatic switch to turn it off after a few seconds.
With TV remotes, absolutely.
With computer keyboards, I definitely wouldn't pay extra for backlighting. I rarely look at the keys much anyway, and I don't see myself sitting at a computer in a room so dark that I couldn't see the keys if I needed to look. Why not just have a lamp?
Maybe a little bit, but I think a small led bulb could light all the keys enough, and then turn off after 5 seconds. If it did drain too much, a recharge dock wouldn't be a bad idea though...I remember the old Nokia cell phones would light up the keypad when you touched a key. That would be nice on a remote control, but it would consume some batteries.