The biggest difference for me is that I'm now much more mobile. For some reason, the simple act of getting up out of a chair is a significant barrier for me, to the point that I'll be stuck in my chair all day, forsaking food, until I am forced by urinary needs.
But standing at my computer, my entire life exists on a single eye-level plain. The activation energy of rising from a chair is no longer a barrier. I step, pace, turn around. I walk out of my office every 15 - 30 minutes, usually just to look out a window and then promptly return. I talk to my colleagues more. And my body stays warmer; I used to wear knit caps all day in my office, but no longer.
A couple of other thoughts:
Legs swelling is a serious problem. The first clinical symptom is pitting edema, and the severity shocked me when I first noticed it. Turns out, your legs depend on regular contractions by the big skeletal muscles to pump blood back up toward your heart. Your veins are equipped with check valves for this purpose. Standing still puts the worst possible stress on these veins, as it both maximizes hydrostatic pressure and robs them of the muscle-pumping. I don't know how to stop this other than to wear compression socks, which in turn requires me to always wear pants to appease my vanity.
The low-back pain I had from time to time previously is gone. Not just better, but gone.
I had a lot of low-back fatigue (different than the chronic pain that previously afflicted me) for the first two weeks, roughly. After my back got stronger (or something), I can now stand for as long as I want. I'll work a 16 hour day with zero back fatigue. I do get minor pains in my feet and more significant pain along the medial aspect of my right knee, which I think is an old MCL injury that's being aggravated by my pronating foot. The more I move, the less these are a problem.
Edit: I use wire shelves, like a bread rack, for my standing desk. The kind where the shelves are adjustable in 1 inch increments, and you can add as many shelves as you want.