I just bought one of those electric sit-stand desks and they're really good (for me anyway).
1) I had a niggling shoulder problem, just a slight discomfort that I was getting every morning when I naturally slumped over my desk. Yes, I tried sitting upright and but my body soon started slumping again. The sit/stand desk sorted it within one week.
2) Trading, or watching the markets standing up perhaps gives a feeling of being 'on top' of things, basically more professional.
3) I'm not a good person in the morning even though I always get 8 hours sleep so standing in the morning is a help
4) Burns some more calories. 150 extra calories a day (more than you need) over 365 days is 14 pounds excess in weight over a year. This is the main reason people put on weight, it's not because they eat too much (some do of course), it's because they eat just a little bit too much over long periods of time. So conversely 150 calories minus every day loses you 14 pounds over the year. That is the 'secret' to dieting, no dieting, just a small tweak to your diet/lifestyle. How many more calories does standing up for 5-10 hours use, I reckon in the 50-100 range. Then cut puddings out and you're there, or hit the gym to work another 150-300 calories off. Folks, this is NOT calorie counting, we all know where they lie, so use common sense.
5) If you have a lot of kit on your desk make sure if you buy a sit/stand desk it can hold at least 100KG
6) In the UK I bought this one -
http://www.conset.org.uk/product/prodone/3825/default.aspx Took about 30 mins to erect.
7) In the US these look good -
https://www.myupdesk.com/
Overall I'm very happy with the result and advise some of you thinking about making the move to do it. There's a good market for these things so if it doesn't work you can shift it online quickly and take say a 50% loss.