Here's a great article on the benefits of standing desks from Smithsonian Mag.

There was a time when standing desks were a curiosity—used by eccentrics like Hemingway, Dickens and Kierkegaard, but seldom seen inside a regular office setting.That's changed, in large part due to research showing that the cumulative impact of sitting all day for years is associated with a range of health problems, from obesity to diabetes to cancer. Because the average office worker spends 5 hours and 41 minutes sitting each day at his or her desk, some describe the problem with a pithy new phrase that's undeniably catchy, if somewhat exaggerated: "Sitting is the new smoking."

As with pretty much everything in life, balance is the key. This Time article explains that both sitting all day and standing all day are bad for your health.

Scientists at the Pennington Biomedical Research Center in Louisiana analyzed the lifestyles of more than 17,000 men and women over about 13 years, and found that people who sit for most of the day are 54% more likely to die of heart attacks.

ReadWrite did some testing and found these results on standing for part of the work day.

10% boost in productivity.
Higher energy levels.
Higher concentration on tasks.
Fewer headaches.

My standing desk is a little wobbly but I already had it for use during recovery from knee surgery and I'm fairly used to it now. You may want something more solid if you are seriously considering this for part of your work day. I highly recommend it but want to stress that the key is balance. Standing all day is very bad for you. Sitting all day is very bad for you. I will sit for about 70-80% of my office time and stand for the rest. Getting up and walking around is the best thing you can do for your health at work. Using a standing desk periodically helps me do that more often.