Did you notice the exercise (stability) ball where the chair should be at my new desk? That was mostly there because I was being silly. This ball is too small for my height (See the table to right to find the right size for you. If you are long legged like me you might need to go up a size because it is more about keeping a right angle at your knees when you are sitting.) .... but it is an interesting concept that I've tried in the past and plan to try again. Here are a few benefits that come from using the ball as a chair:
If you want to try, ease into it. Believe it or not you will be really sore after a full day. Maybe try an hour out of your day at first, then two and work your way up.
If you have to sit all day for work, at lease make a workout out of it!