I consider myself to have Delayed Sleep Phase Syndrome (http://en.wikipedia.org/wiki/Delayed_sleep_phase_syndrome), though whether it should qualify as a "syndrome" is debatable. I don't need more sleep than the average person, I just need it later in the 24-hour cycle. I wouldn't be surprised if many/most hackers are the same way.
I read an article that blue light can cause delayed sleep. Apparently, it interferes with the evening release of melatonin, a hormone that regulates sleep. The article speculated that the common perception that hackers are night-owls could be caused by staring at a monitor with blue backgrounds, etc. I don't know if its true.
Emissive light sources in general interfere with melatonin. I have a severe melatonin deficiency and I find that avoiding TV, monitors, and bright lightbulbs for an hour before bed helps tremendously in my ability to sleep, in conjunction with a synthesized melatonin medication (Rozerem). Books (and I imagine eBooks with eInk) are fine, but the laptop is not.
DSPS makes maintaining a normal 24-hour schedule painful. (Imagine having to get up one hour earlier every day! That's how a 24-hour schedule feels to me.) I have it and it takes a lot of self-discipline to hold down the 9-to-5 schedule. But it is possible with the right techniques.
More info on my experiences at http://news.ycombinator.com/item?id=205179 .
This is an interesting look on it... didn't know it was actually a classified disorder. While my sleep cycle is pretty mixed, for the most part I can't sleep during the normal phases of the 24 period. Further, I don't have an exercise problem... I just do it whenever I feel up to it. My sleep cycle started to change rapidly when I worked the graveyard shift for my first professional job... did that for about 3-4 years, which really messed me up sleep-wise.
The one thing I love about night-hacking is the serious lack of distractions. It assists me greatly in concentrating... at least in my neck of the woods there is less distractions.
