I use a standing desk at work. Yes, all day. And, yes, I can still sit down—it’s not as though I took a vow of standing or anything.
A friend of mine mentioned that he uses one, loves it, and no longer suffers from the dreaded afternoon sleepy time (official term). So when I spotted one at work, I asked if I could use it and have been standing ever since.
If you’ve been considering it, I will say that the first few days are not pleasant. First, your back and feet hurt. Second, you get snide comments from everyone, like “is this the Apple store help desk?” or “He’s standing up for what he believes in … being a @$$#*&#” And third, you won’t have as much surface area to put folders and papers and such.
As for the benefits of standing, these artist’s renderings should suffice.