I'm 6'3" (~190 cm) tall. At my last job, I was having severe leg pain from sitting at a too-short desk, which caused me to sit with my legs tucked under my chair all day. Since there was No Money™ to buy another desk (and I rejected the suggestion that I move my existing desk up on top of a pile of cinder blocks), I blew ~$1000 of my own money on a GeekDesk adjustable height desk.

Despite using the desk for a year and a half, I couldn't stand at it for more than an hour or so without back pain. To me, the real benefit of the adjustable height desk was being able to raise it up to a comfortable height for sitting -- I could finally sit with my feet flat on the floor in front of me!

A few months later, after a company in the university's research park folded, we got to pick over the bones and grab some office furniture. I managed to get a rolling, armless, adjustable height drafting stool. The combination of the GeekDesk and that stool was nirvana as far as sitting in an office goes -- I was able to leave the desk at the same height whether I was standing or sitting on the stool, which made it easy to switch back and forth throughout the day.

One downside to the desk: since most people I worked with were shorter (sometimes significantly!) than me, I often had to temporarily lower my chair and desk so other people could easily see something on my computer screen. On the other hand, it was easy (and rather awesome) to have conversations with coworkers who were roughly the same height as me -- I just stood up, pushed the chair out of the way, and had room for a standing conversation with two other people who could all see the screen.

How long do you use a standing desk at a time? After a while, my back and legs start to hurt and I need to sit down.