My laptop won't boot Natty beta 2 unless it is plugged in most of the time (like 2 out of 3 times). After it is booted I am able to unplug it and let it run on battery power with no problems. Sometimes I will be able to boot on just battery power, other times it will hang at either a blank, purple screen right after grub2 or at the flashing "_" screen.
My laptop is a Lenovo Y460.