I can't remember where I saw this mentioned....I've been racing through my feed reader these past few days, but I've installed f.lux, a little piece of software that changes the colour of your computer screen in sync with the day.
From the website:
f.lux ... makes the color of your computer's display adapt to the time of day, warm at night and like sunlight during the day.
It's even possible that you're staying up too late because of your computer. You could use f.lux because it makes you sleep better, or you could just use it just because it makes your computer look better.
f.lux makes your computer screen look like the room you're in, all the time. When the sun sets, it makes your computer look like your indoor lights. In the morning, it makes things look like sunlight again.
Tell f.lux what kind of lighting you have, and where you live. Then forget about it. F.lux will do the rest, automatically.
I've been using it for a couple of days now and it's definitely nice to get a warmer, somehow sleepier colour later at night. Right now, it's just after 11pm and my screen is a sort of pale orangey-pink. Check it out here. It's available for Windows XP/Vista/7 and Mac OS X. There's also a Linux version.