I have the poorest posture and form when I'm on the computer. I'm pretty sure I don't follow the correct way of typing (this finger goes where and whatnot) either. So, I am more or less just like any average computer user.
Unfortunately, I've experienced the downside of being so careless with my posture and form. The day before my wedding (oh, yes, I got married! But that's for another few more posts) I was feeling some pain on my right arm, running from my wrist until my elbow towards the inner part of my arm. The pain was tolerable so I thought it might just be because of the pre-wedding stress or I was tired.