Funny, I was just exploring alternative options for my office.
I hate chairs. There is no way anybody use chairs "as intended", e.g. straight back etc. It just doesn't work. Sooner or later you'll crumble in one way or another.
I'm 34, but I've been working with computers for 16 years. Right now I have pain in my left arm, and tickling in my fingers. Probably injured nerve in my neck or sth.
Besides, posture is very important also for the mind. Good posture = better concentration. Buddhists, zen-Buddhists and yogis have figured that a long time ago.
This seems an interesting alternative: http://www.zafu.net/zenoffice.html Not really expensive. I might just order it and try it. I find seiza position quite comfortable, but haven't found any studies on long term health effects. It could slow down blood circulation in legs, which again is not very healthy.