I saw this thread and just had to register just so I could say: I've owned my business 20 years this March, working at the computer constantly, and have always wanted to stand up.
A couple years ago I started surfing the net looking for "adjustable height" desks. The only ones I could find that are real desks (besides those narrow non-adjustable standing "work carts") were being advertised at $3000 and up, which was hard for me to justify just for a desk.
Then, last March, Ikea opened up their new warehouse in my town and my wife and I did the obligatory new-store walk-thru. I said to her when we were walking thru: "I wonder if they have any adjustable desks?" Right then (no kidding) I turned around and squinting across the massive landscape of Ikea, I saw a very tall table that I though could possibly work as a desk. Sure enough, it was a desk, and the best part is it was height-adjustable with an electric motor. Plus, there's an optional "basket" to bolt to the underside of it to put your computer in, so you don't have to worry about monitor/speaker/keyboard wires stretching when the desk is raised. The best part is that the tabletop + adjustable motor system was about $600, a paltry fraction of what I'd seen elsewhere. I think the Ikea style line is called "Galant".
I know this sounds like an Ikea commercial, but I swear - I don't even like Ikea's general "quality", like for general furniture. But I've been standing since last March and my butt is finally not numb anymore (I'm 6 ft. 4 in. and thin, so my circulation isn't that great even though I exercise all the time, and sitting down for long times makes my legs fall asleep and my lower back ache).
Now when I go home, I can actually sit comfortably at the dinner table. I used to lie on my stomach on the floor to eat dinner, just to get off my sorry rear.
What's really cool is that sometimes in the afternoon after standing all day, I just lower the desk with the button and presto, I'm sitting in my chair again. I've always said, the only perfect working position is one of CHANGING POSITION. For example, now that I have this tall desk, when I'm on the phone with a customer I'll leave the desk up high, walk across my office with my wireless phone headset on, sit in my (low) office chair, and prop my feet up on the file cabinet. This gets the blood out of my feet. Five minutes later, the call's over, and my legs have had the perfect break and are ready to stand again. I can't figure out why more people don't crave this type of arrangement. Maybe it's the being tall/skinny thing, or maybe people don't have to be stuck at their computer like I do.
I could go on and on about this and it probably sounds silly, but it's a huge QOL difference (quality of life). Here's another example of how big a deal this is for me, and then I'll try to shut up: It used to be that when we would go on driving (or flying) trips, I hated it because sitting in a car/plane for hours on end, after sitting at work all week, was torture. I never sit at work anymore, so now, sitting down for a trip is actually a restful thing, and a change.
One more note: the Ikea desk is simply a tabletop with legs, so don't expect an executive desk or something. But at least the electric motor + legs assembly is modular so that when you're buying it, you can choose from several different shapes and colors from their tabletop line.