http://stereopsis.com/flux/
Just learned about this the other day, and I rather like it. Basically, based on your location it knows sunrise/sunset and so it adjusts your screen brightness between night and day so that it always remains at a pleasant level. I have pretty ambient lights in my room, so once it gets dark my screen is especially bright. It's supposed to make it easier to sleep as well, because you haven't been subjecting yourself to such a bright light right before bed. It seems a bit brown at first, but you soon get used to it. Set it to change over an hour rather than 20s and you won't even notice it.
Just learned about this the other day, and I rather like it. Basically, based on your location it knows sunrise/sunset and so it adjusts your screen brightness between night and day so that it always remains at a pleasant level. I have pretty ambient lights in my room, so once it gets dark my screen is especially bright. It's supposed to make it easier to sleep as well, because you haven't been subjecting yourself to such a bright light right before bed. It seems a bit brown at first, but you soon get used to it. Set it to change over an hour rather than 20s and you won't even notice it.