|This graphic demonstrates the dangers of sitting at your desk too much and too long.|
Me, I wasn't influenced by Ernest Hemingway. It was much more basic: I got the standing desk because I didn't like sitting at the keyboard for long periods of time (in the words of author Robin Lee Hatcher, I was getting "numb butt").
I also appreciate the warnings that are now coming out like this one at Boing Boing: sitting without getting up for breaks is bad for your body. As in, sitting for many hours at a time, as a routine practice, is extremely bad for you and causes all sorts of problems with your gastrointestinal system, your heart, and other things. Beware.
So, standing desk or not, get up if you're at a computer right now and move - or at least, stand.