That whole "good posture" thing is future physical problems waiting to happen. For 25 years, I've always put my feet up on the corner of my desk (to the left), set the seat as high as possible (or adjust the desk lower) and lean back, arms extended. Basically, I'm positioned like an F1 driver in a cockpit.

No back problems as there's no weight on my spine. No carpal tunnel issues, as my wrists are always flat. No fatigue from holding my body at right angles for hours at a time.

The downside is I look like a total slacker in the office, especially to narrow minded image conscious managers who expect me "to act professionally."