I only got up an hour ago, at 9pm... when I have nothing to do during the day my sleeping pattern inevitably becoems nocturnal. Also my circadium rhythm seems to be about 30 hours long, so after a few nocturnal days I'll get up and not sleep for 2 days and "reset" my pattern back to nighttime life.
Advantage: Nocturnal is very yummy lifestyle. "I write by candlelight"
Disadvantage: My feet get cold if I don't bother to put socks on.