I know it's not just me and I'm not trying to act as if I'm a special case, but the biggest problem I see w/ office chairs is they don't support a proper posture while sitting at a computer. For instance, I often find myself slouching or trying to reconfigure my arm-chair height so I can jump from the keyboard to the mouse w/o much effort.
Again not to sound like a special case, but I have extremely long legs (high-waist line, like a woman...) and short torso, I don't know if this physical feature is affecting my posture in normal office chairs, but Aeron seems to effect my posture enough that it makes a huge difference.