Back problems
randallsquared: I would have assumed that the reverse would be true: people who mostly sit all day should have less back pain.  In my personal (apparently anomalous, given the posts here) experience, this is the case.  When I worked in manufacturing 12 years ago, putting commercial refrigerators together, I had back pain quite a lot, even to missing some work due to it, but since I switched to desk jobs, it just went away.