Running Mavericks 10.9.2 latest beta, pmset -g shows: Battery Power -1* AC Power -1 Currently in use: standbydelay 72000 standby 0 halfdim 1 sms 0 hibernatefile /var/vm/sleepimage gpuswitch 2 disksleep 0 sleep 0 (sleep prevented by AddressBookSour) hibernatemode 0 ttyskeepawake 1 displaysleep 4 acwake 0 lidwake 1 Does anyone know what "sleep prevented by AddressBookSour" means? Update 1. AddressBookSour seems to be an abbreviation for AddressBookSourceSync. The link shown below has a method that didn't work for me, but a Google search turned up a suggestion to reset the iCloud settings. I have never even used or set that up, but after trying it, and signing out immediately, that "sleep prevented" msg disappeared. Apple really has dropped the ball on this one. Not everyone even wants iCloud enabled! And linking such basic functions as sleep on a MBP to iCloud is beyond ridiculous. /end rant Thanks anyway FreakinEurekan! Update 2. Same issue appeared on my Mac mini, but sleep still works, despite the warning shown by pmset -g.