[mikekchar]

Same. I bought a $10 stool as we had just moved (without any furniture) and I didn't want to rush into buying an office chair because I knew how important it was to get a good one. 7 years later I was still using the stool (though I added a pillow). Last year I replaced it with a dining room chair (which I had bought when my parents came to visit -- we don't actually have chairs in our house and sit on the floor, Japanese style). It's nice to occasionally sit back and rest my back, but I'm not necessarily sure that it's a good idea.

The main thing that makes the biggest difference for me is that my keyboard and monitor are at the right height. Which is to say that I have an external keyboard (elbow height) and my laptop sits upon a series of cardboard boxes so that the top of the monitor is at the same height as my eyes. I also use a trackball at elbow height that I can reach without moving anything unduly.