I think more people should be aware of the health risks from sitting at a desk for long hours. You can destroy your back and wrists among other things. It's worth upgrading to ergonomic hardware so that you can keep yourself going and not have to take breaks away from your profession. Ergonomic keyboards are great and easy to get used to as are the mice. If you're using a mouse buy an ergonomic mouse mat, they're very comfy. I've noticed recently after transferring to using a Wacom to animate with that I'm getting a bit of ache in my wrist and am thinking about getting one of these wrist wrests (since I wrote this draft the ache has completely gone, must have been my wrist teething).
A good chair is important too but they can become quite costly. Also don't forget that your monitor should be at least arms length away from you so that don't destroy your vision.
It's not just about having fancy hardware that helps your body bits out. You need to make sure that your diet doesn't suffer too. I often fall into the trap of eating anything so that I can get back to my work and my body soon lets me know when it's not appreciating it. A well balanced diet is incredibly important, all the time. No excuses. As well as the diet we have exercise, even if you're getting up to walk around every hour or so. It's better than being sat down in one (often awful) position all day.
In conclusion, unless you want to be a crazy blind hunchback with broken wrists and malnutrition then be nice to your body and it'll return the favour.
Victor Navone (Pixar animator) wrote a tutorial about ergonomics a while back, check it out here - http://blog.navone.org/2007/12/ergonomics.html