I work nights, so when I get home at 6am I turn it on, play with it for a few hours then go to sleep and leave my comp on, screensaver comes on in 15min, and when i wake up around 4pm i play with it again for awhile then i turn it off when i leave for g/fs and work. So its only off really when im not home.
Although, when I wake up i restart because it seems to be slower after being on for 7 hours and not doing anything.
My last comp that i tried to put to sleep it froze. ive heard bad things from all sides, leaving it on, turning it off, putting it into sleep mode.