Re: Since I began using computers, I have hurt my:

[wolfger]

Hearing??? How about eyesight! Many more of us strain our eyes looking at the screen for hours than batter our eardrums with oggs and mp3s. (Or maybe I'm just sensitive about this because I'm getting my first pair of glasses now, after too many years of geekery).
I voted chair, since I'm heavy and tend to demolish the poor things. Sleep pattern was a close second, though.