so....if you have a standing desk maybe the point is that you walk around more, whereas when one sits one is less inclined to get up for a minute walk.
I tried a self-made standing desk for a couple days but went back to sitting because I couldn't take the standing for long periods of time.
Here's my desk: http://rwmj.wordpress.com/2010/01/25/treadmill-desk-part-6-h...
Have a look at these products http://www.leuwico.com/web_e/products/office_furniture/ergod...
The height can be adjusted either manually (hydraulic system) or with a motor. It works better than it sounds. You can adjust the height even with a loaded desk easily.
The only question is: Would I remember to change my posture regularly?