I saw the principle some years ago, when I worked with a colleague on his computer on a software documentation project. After 45 minutes, his computer would block access to his data, "forcing" him to take a break. Now I see this more and more often; Workrave can even propose you exercise for your hands, body and eyes. Why have we become so undisciplined about our health so that the computer has to remind us we have life outside of the net and work?
Workrave suggests that every 10 min, you close your eyes for 30 seconds, every 45 minutes, you take a 15 minute break. It gives you also a daily limit of your life-on-the-screen.
"Take breaks. Grinding away at a task for hours on end, you'll lose perspective and eyesight. As Lincoln said, if he had to chop down a tree, he'd take breaks to sharpen his ax. I use a free computer program called Workrave (www.workrave.org) to remind me to look away from the screen and walk around every so often. Just knowing that a nap, a vacation, or a meal is on the horizon can make me more productive and not look for excuses to take little breaks all the time."