If you sit at a desk for hours every day, you've probably felt some pain in your lower back at some point. It's not surprising that sitting so much is actually pretty bad for you. About 10 months ago, I started experimenting with standing desks, and it has turned out to be one of the best things I've done regarding my work environment and posture. My back feels great, I have more energy and I even remain focused for longer periods of time.
I am always talking to people about standing desks and they are usually very interested in getting started but think it is too expensive. Nonsense! You can set up a desk with things you have laying around the apartment / office. Cardboard boxes, cheap freestanding shelves, milk crates, textbooks, pianos, etc. Do whatever it takes to get something set up, even if it is temporary. At least you'll be able to get a feel of what it's like before you make any further investments.
It's pretty easy to get the basic guidelines down pat. Make sure your keyboard is set at a position where when typing, your elbows are at a 90 degree angle and your wrists are resting flat. This will probably mean propping up the front side of the keyboard slightly, unless you have something like the Microsoft Natural Ergonomic 4000 (which I love). Your external monitor (or laptop screen) should be positioned so that you are looking directly forward, or very slightly down. Don't keep it down by the keyboard, you want your head up. If you use your mouse often, it can be mounted at the same level as your keyboard. I usually keep mine to the side, in reach but out of the way.
Standing constantly will take some time to get used to. I started with 1 hour long periods of standing 2 or 3 times a day, while sitting in between. Over time I could stand longer and it would take longer and longer for my knees to get tired. At one point early on I picked up a tall stool to make transitioning between sitting and standing easy. After about 3 months I was in the groove and standing the entire day. My lower back pain was gone and my legs felt much less restricted. I used to have the urge once in a while to get up and walk to stretch but now that I'm standing all day, I no longer need to.
Living in New York, my legs had gotten used to walking everywhere. I heard mentions of treadmill desks, and figured I'd give it a shot. $50 in hardware and two weekends later, it was up and running. My boring treadmill had been successfully converted into a fire breathing code factory. My optimal speed seems to be around 2.6mph with a 30 minute break every 2 miles, but you'll need experiment to find what is right for you.
If you end up giving it a shot, please send me a photo! I'd love to see what you come up with. Enjoy your healthier, more comfortable workstation!