I'm the first to admit I have a cushy office job. I sit practically all day from 10-6, and by definition, I'm probably leading a sedentary lifestyle. I'm lucky to live in New York City, so I get a good amount of walking in every day, but I am not the pillar of active living by any means.
If you work a job where you have to be on your feet for hours on end, you probably wish you were in my shoes. Sitting all day might be harmful to your health long-term, but running around all day doing silly little tasks for a company hurts your body immediately. When you get home from work, all you want to do is lay down because you weren't allowed to sit for eight hours. One job took this a step further and threw out chairs to prevent employees from sitting on the job.