I naturally fall into the habit of being up late into the night, and this is usually when I am the most productive. However, I have recently started (2 months ago) a health and wellness program of my own design which incorporates proper nutrition, exercise, stress reduction (yoga, hot tub), and proper sleeping habits. As a result, I have been going to sleep between 11pm and 1230pm most every night, and waking up naturally at around 8.
I must admit, although I rather enjoyed what I accomplished from being up at night, I much prefer how I feel during the day when I get a proper night's sleep.