I built myself a standing desk and used it for a couple of months. It was my feet, not my back, that convinced me to go back to sitting down. I suppose if I'd invested in some kind of special flooring or even more comfortable shoes, I might still be using the standing desk, but I don't know.

What I'd really like is some way to sit on an exercise bike (I believe they're called "stationary bikes" in some places) and still be able to use a keyboard and mouse. Not sure how that would work, but if I could figure it out I'd be rich and skinny before you know it!