This Time magazine article from 2011 explains the health benefits of standing at work, and also provides some of the arguments against it.

It’s easy enough to buy a new standing desk — see a selection here — or you can try to convert an existing desk. Switching to a standing desk can take a little adjustment, especially for your feet, but many of those who’ve tried it say they’ll never go back to sitting down.

Like many health trends, however, standing desks can cause problems if they’re taken too far. For one thing, not every researcher has found that stand-up desks are a cure-all. Scientists in the American Journal of Preventive Medicine examined 17 studies on occupational sitting and cancer, and found little to no connection. And some experts in occupational health worry that hours of uninterrupted standing could be bad for your body. (More on TIME.com: Walking While Working)

Ultimately the article says sit-stand desks are fine, but walking is also an important part of a healthy lifestyle:

Research shows that you don’t need to do vigorous exercise (e.g., jumping jacks) to get the benefits; just walking around is sufficient. So build in a pattern of creating greater movement variety in the workplace (e.g., walk to a printer, water fountain, stand for a meeting, take the stairs, walk around the floor, park a bit farther away from the building each day).

More articles about standing are in my Standing stash:

http://pandawhale.com/ifindkarma/standing