Err... Android does 'hibernate' by default, pretty much any time that the screen is off and no applications are actively waking the phone up, or keeping it awake (Taking a 'wakelock'/'keepalive') it will put the processor into 'deep sleep' mode. There is a bug with Samsung's firmware on apexq that will prevent deep sleep occassionally if the phone is booted while plugged in. Just remove the cord while you reboot, and there should be no issue there. The bigger issue is running things which actively keep the phone from sleeping consistantly. Unfortunately these days this includes Google Services by default now. I've seen it take wakelocks THOUSANDS of times throughout a day. In OmniToad we added mechanisms to prevent that, in CM based images Privacy Guard does a decent job if you toggle off Google Services' ability to wake the phone off and keep it awake.