Health and Safety 2 Interesting article about one reason for not spending too long in front of your computer:
http://news.independent.co.uk/uk/health_medical/article2021203.ece

"So what is a visual migraine? The textbook description says it is a temporary visual disturbance caused by a vascular spasm in the brain, similar to the conventional migraine but without the headache because it affects a different part of the brain. In the case of a visual, or ocular, migraine, the spasm results in decreased blood flow to the occipital cortex, the bit of the brain that deals with vision. [...] Visual migraines, in particular, are associated with stress and fatigue and/or hormonal changes. [...] muscle tension in the neck and shoulders is a common contributory factor, since it constricts the blood supply. Anyone with a history of this sort of problem who works hunched over a computer, especially under pressure, is a prime candidate for a visual migraine ..." The Independent Extra Tuesday 28th November 2006

Following on from the previous health and safety entry
Microsoft has guidelines for the healthy use of computers.  ¶ 10:33 am