Reported by Nofearl, Sep 16, 2012

On Mountain Lion, using darkwake=0 disables the autosleep. When I 
use the darkwake=0, the system (almost) never automatically sleeps. 
And when I remove it, it sleep every time without a problem.

But, the reason I use the darkwake switch is, without 'darkwake=0', 
the lights&fans kick-in when I try to wake it from sleep, goes 
back to sleep in ~5 seconds. I've accidentally found that if I press 
the power button second time during that ~5 second period, it wakes 
up and monitors/system came online.