Sitting for a very long time is bad for you. It causes increased chance of death, causes your back to hurt, makes you fatter, and lets your energy level go down after hours of doing it.

It's not so much the "coding" part as the "sitting at a desk for 10+ hours a day" part that makes standing desks so attractive to programmers.

http://pressroom.cancer.org/index.php?s=43&item=257

http://www.medicalnewstoday.com/articles/175656.php

I haven't done it a lot, but I like to pace when I'm thinking about a hard problem. Having my computer at standing height means I can go straight from thinking through the problem to coding the solution without the attention shift of settling back down to a sitting desk.

Reportedly, there are also health benefits to standing rather than sitting.

There is a lot of discussions about this on Hacker News and generally people who work standing are happy about it.

See eg http://news.ycombinator.com/item?id=2828948

For more http://www.hnsearch.com/search#request/submissions&q=sta...

Here's a write up I did, that includes more links on why I switched to it: http://jessenoller.com/2011/04/25/switching-to-a-standing-de...

I switched to a sit-to-stand desk for comfort.

Buttocks and legs would get sore if I sat too long a day. I only learned about it being healthier for you after I started using my desk.

I alternate every hour or so for an hour.

I started standing about 2 months ago, mostly for the supposed health benefits, and really like it. The anti-fatigue mat and adjustable desks really helped me get going. I started one week at 2 hours of standing a day, then 3 hours the next, etc., up until I was standing all day long.

I don't know that I necessarily code better when I'm standing, but overall I prefer it to sitting.

When I worked at bigcorp, inc., I used to always prefer going down to the datacenter and working on my projects at one of terminals in the racks, standing of course. No cubicle distractions, no noise except the constant hum and the occasional greybeard shuffling by, standing kept the blood flowing better, and all of it helped me get into and stay in flow better.