No, I don't know anyone who suffered from RSI or SAD
I'm a secretary, and I sit in front of my computer a lot of time, Normaly I get up a lot of times during the day.. but at night sometimes I have headache. I supose that I don't sit correctly, but it's very difficult becase there are a lot of things to do, telephone, mouse, talking, write...
If you have a pain in the back, it's necessary to do some exercise during the time in your work, for exemple..slowly bend your head to the left, and to the right. And it's necessary to move the legs, get up every hour, to do pothocopies, or.. to go to the bathroom...
I think that the exercise described in the reading are effective, but sometimes it's very difficult at word to do them, because there are a lot of work... and.. it's difficult.
Normaly I get up sometimes to my chair,, for move my body.