Stand-up desk

Stand-up desks are growing in popularity for a variety of reasons, such as helping back pain (mostly anecdotal evidence) or reducing sedentary time to burn extra calories (1/3 more calories per minute burnt compared to sitting desks). The benefits and risks of standing desks have not been explored rigorously, although on a related note it is well established that sedentary lifestyle leads to health problems, and that even little movements throughout the day help. In light of this, I would like to share with you a helpful insight I received from a reader of this blog. I thank the reader for kindly allowing me to post it here.  (The abbreviation "40$SD" below refers to the The $40 Standup Desk.) 

Stand-up work has helped me a lot, I think. Now I have stand-up workstations both at work and at home. For my home station, I just replaced one of the shelves above my desk with a double-depth shelf (basically, I replaced the original 9" horizontal brackets with 19" ones, and added a second 10" shelf in front of the first one). I like the shelf approach, because it gives me more options for vertical adjustment [than does the 40$SD], and it's not much more expensive.
Even with a standing desk it is difficult to achieve the proper vertical placement of the screen and the keyboard. For example, the setup shown in [the 40$SD blog post] seems wrong to me: the keyboard is too high and/or the screen is too low. I want to have the screen at eye-height (more or less), and the keyboard placed so that my forearms are at an angle slightly greater than 90 degrees when I type (i.e. so my wrists are slightly closer to the floor than my elbows are).
At work I achieved this by having a tray for the keyboard that hangs from the bottom of the desk top, so that the plane of the keys is about 5 inches below the desk's top surface. In addition, I had to prop the screen up (I put it on top of an over-turned plastic bin) so that it would be at the right height. The arrangement is still not ideal, unfortunately, because the surface of the desk is a bit too low for me to write comfortably on it while I stand. To achieve the optimal arrangement I'd need to find some other way to hold the keyboard up at the current (proper) height that is not constrained by the height of the desk top (as it is now).
For me the benefit of the standing desk is simply that it has helped me reduce the total number of hours that I spend sitting down. This is the goal, which means that I not only stand while I work, but also while I read, while I surf the web, while I watch videos, etc. Of course, this is as tiring as you can imagine. Both at work and at home I have high chairs that I can use when I start getting tired, but they are not comfortable, so I end up not using them a lot.
(One unintended benefit of this new arrangement at home is that it has reduced the amount of time I spend idly surfing the web, without in any way limiting my ability to use the web when I need it. It boils down to this: the new setup is good for work, but not good for relaxing. This led me to a counterintuitive realization: "comfortable seating", which at least our culture considers the ideal to look for, is actually a health hazard. Whenever we opt for comfortable desk chairs, or comfortable sitting furniture in general (couches, recliners, la-z-boys, you name it), we are basically setting traps that lure us into spending unhealthy amounts of time sitting down. It is not surprising that we so readily stay in stationary positions for hours at a time. I think one can make a good ergonomic case for a hard, wood or metal chair (or stool, or bench), because the best chair is the one one doesn't use too much!) 
Also, I actually had to modify the way I stand up, because the "old way" was beginning to give me knee pain. My physical therapist advised that I should not lock my knees, but rather stand with them in a slightly flexed position. The flexion of my knees when I do this is very slight, and it would be difficult for any one else to notice (for example, even though my knees are slightly flexed, my head is at exactly the same height as it would be if I lock my knees). This got rid of the knee pain, but it takes some extra effort.
I think that it is a very worthwhile change for you (anyone with a desk job) to try, even if you didn't have any back problems. But in any case, be ready for a fair bit of tweaking and experimentation. And above all, keep reminding yourself that the primary goal is to reduce the number of hours you spend sitting every day, and the standing desk is only one of several measures one can take to that end.
On a related note, as part of re-learning how to stand, I also have had to learn to avoid positions like contrapposto (in which I shift most of my weight to one leg and hip) because they invariable overload some ligaments (when I relax into one of those positions I am basically asking some ligaments to do more than their fair share for keeping my body upright.) These are all one form of slumping or another: one relaxes a set of muscles by shifting the load on some other set of joints and ligaments. Of course, as one gets tired from standing up, one naturally gravitates (literally!) into such slumping positions, so it takes effort to avoid them. This issue is particularly important for me, because I happen to have hyperflexible ligaments (which is also the reason why it takes more energy for me to keep good posture, since I can do it only through active muscular contraction, rather than through passive ligament tension). It may be less of an issue for people with less flexible ligaments. (Then again, for all I know, people with stiff ligaments may be less susceptible to the hazards of "over-seating".)
One last point: the first few days of stand-up work I was exhausted at the end of the day, but over time my stamina has improved somewhat.