178 hours later, the battery finally completely drained (oh how I love the battery on this thing!) ... but I digress...
I let it charge (while powered off), than turned it on - I was at the same, middle of the road, brightness setting as I had been before I'd let it die.
So...could an app you have installed be the culprit?
Next Phone: Your guess is as good as mine!
Nook HD+: Rooted, no need to ROM.
Atrix 2: Rooted, soon to be retired.