I'd like to add that you can easily elevate your monitor and keyboard and work while standing. I spend hours at home at my computer, standing. I have built a platform on the 'desk' with a plastic stepping stool topped with a briefcase that provides the surface for my keyboard. The monitor is on top of the computer which is on top of something else, which is on top of something else - you get the picture.
I have a feeling that it would be accomplished more elegantly in an office.
I stand and stand. This results in swollen ankles after a certain amount of time. My podiatrist says it's gravity that is doing that. I sit down from time to time, to take a break. I guess if I worked in retail and had to stand all day, it would be the same.