A lot of office chairs enforce a sit-up-straight posture which I really don't like. When sitting at a computer for long hours I like to lean the chair far back and put my feet up or out in front of me. I've found that I never get back or wrist pain this way and have run across some articles that say this is better for your back.

http://www.medicalnewstoday.com/articles/57654.php http://rsna2006.rsna.org/rsna2006/V2006/conference/event_dis...

The only downside is that many people will associate leaning back in your chair with your feet up as being lazy. For this reason I printed out that article and pinned it to my cubicle wall.