I had a harrowing day today at the emergency room. All is well -- better safe that sorry -- but at the very least, let it be said that I should mitigate against eye and neck strain.
Coming home, I re-installed a piece of software I once used: Workrave. It forces you to take short pauses and coffee breaks, and leads you through stretching your arms and shoulders, and refocusing your eyes. You can set the length between breaks and how many times you can defer them, say if you're on deadline or showing someone something on your computer.
For users of the newest (Oneiric) version of Ubuntu Linux, install the backports repository (Edit > Software sources > Updates tab in the Ubuntu Software Center) and install it there or any standard way.
Linux users who compile from source and Microsoft users can get their software here.