I have had some minor problems with RSI, and would like to prevent any more. I have a seriously radical keyboard, and I use a keyboard timer, a program which reminds me to take frequent breaks. On Linux and Windows, I have been using WorkRave, which is fantastic. However, I was without a timer on Mac OS X until I recently found AntiRSI. It is unobtrusive, configurable, and is as pretty as a Mac application could be. It has found a permanent place in my dock. Highly recommended.