I enjoy the Mac OS X brightness auto-adjustment on my MacBook Air, but I would usually prefer the screen dimmer than the level it decides on. This would also conserve some charge.
I don’t suppose there is a way to bump it down a few notches? (I have searched for this and found nothing, so I assume the answer is no. But it is difficult to pick keywords that will produce relevant rather than almost-relevant results so there is a slim chance that I am overlooking it, and I shall remain hopeful yet.)
This would be in 10.7.4, in case that is relevant.