I now have a standing desk and I find that much better than any of the desk chairs I've ever had, including the very expensive Freedom Chair by Humanscale.
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.
I use it all day (maybe 8 hours a day), but I move around a lot. Whenever I'm not typing or reading on the screen (thinking), I walk around. That helps a lot. I sometimes go sit down a bit in other rooms, but basically I can stand all day if I have to.
It took my about 3 weeks to get to that point. For the first few weeks, my feet hurt a lot. But at some point I passed a threshold and it pretty much stopped hurting altogether as long as I can walk around and shift my weight from one leg to the other a lot (I couldn't stand still all day).
I am not Mike. But I use a standing desk. It took me a few weeks to get fully adopted, but now I can stand (or move in place) for several hours, if necessary. Usually I take short breaks though.
And actually, the ability to take short breaks and walk around is something I really cherish. Removing the (small) barrier of needing to get up has really helped.
But you can not read too much into my experience report with the standing desk: I took up weightlifting at the same time I got my standing desk, and so it's hard for me to say which change was responsible for which improvement.
