UPDATED: Apparently not a new feature, it's called Safe Sleep and was also in Tiger. It can be enabled by using a hack such as the DeepSleep dashboard widget. Original post: Just occasionally, I run the battery right down on my MBP in the evening and can't be bothered to plug it in to recharge it overnight. I just set it to sleep mode and usually find it dead in the morning (smart, I know). I did this last night, and this morning I woke up to find that the light on the latch had stopped glowing (presumed dead). So I plugged it into the charger and pressed the power button. IT WAS ALIVE!! The whole of my Leopard screen was displayed in a very strange black & white hue, and there was a progress bar near the bottom of the screen. When the progress bar completed, the MBP sprang back to life where I'd left it. It appears that when the Leopard MBP runs very low in power, it switches to ultra-sleep mode to last longer. I wish I could induce this when I wanted it, rather than it being a hidden feature!