This recent CNN article brings to light some shortcomings of having a standing desk. Prolonged static sitting does has a negative impact on our overall health, but replacing it with prolonged static standing isn't the answer. The article reports that "buying a standing desk may reduce your sitting time by as little as 32 minutes a day." Removing only 32 minutes of sitting from an 8 hour work day is certainly not enough. If your work revolves around long days of computer use, the ability to alternate between sitting and standing is best.
The article offers a suggestion of hourly 2 minute walks or 5 minute jogs. This would certainly be a great way to increase activity throughout the day but for many out there, may not a very realistic option. Additionally, positioning your office chair at a reclined angle may unload some structures but at what cost? No mention is made of global ergonomic setup. Poor ergonomics is a major cause of repetitive trauma musculoskeletal injuries that are costly to treat.
So what would I recommend for the average office worker?
The ability to alternate between sitting & standing AND to do so frequently, every half hour throughout the day (don't wait until after lunch to change position)
Use a chair that fits your body properly for when you are sitting. If you are 5' tall and your coworker is over 6' tall, the same size chair will not work for both of you.
Incorporate mini stretch breaks into your work day. Stretch your neck, back, forearms, legs. You name it. Take 30 seconds while you wait for the printer or fax and use it to your advantage. It takes time to make this a habit but is worth the effort.
Incorporate more movement in the form of walking or stairs into your work day. Instead of emailing a question to a coworker, walk to their office. Take the stairs in & out of the building or if applicable to lunch instead of using an elevator. If your lunch break is long enough, use it to go for a walk and get out of the office.
If you live close enough consider walking or biking to work instead of driving.
Our bodies are certainly not designed for remaining still. In general we all need to move more, not just during the workday. The health of all of our systems (cardiovascular, musculoskeletal, etc) depends on it.