I stand 6-8 hours a day. so do most of my coworkers. Simple observation of a chubby mechanic or a fat construction worker will tell you that the "standing desks are healthier" line is complete bullshit.
The jury is still out, but subjectively, switching to a standing desk at least a few times a week really helped my posture and back.
Here's some brand-new research based on 1000 people wearing accelerometers 24/7: http://epublications.uef.fi/pub/urn_isbn_978-952-61-2928-0/i...
Sedentary behaviour, physical activity, and risk of coronary artery disease and diabetes mellitus
"From the accelerometer-derived parameters of SB [sedentary behaviour], a higher number of daily SB bouts lasting over 10 minutes was the strongest predictor of a high CVD [cardiovascular disease] risk."