I use both a standing desk and a sitting one, and agree with you on the three-week burn-in.

But while the benefits of standing desks are plausible, it is very important to remember that they have an unequivocal, well-documented, peer-reviewed, scientifically solid set of risks associated with them: http://www.hazards.org/standing/

That is, there are well-documented health issues with standing all day, and of course, putting desk after standing doesn't change the physics or the physiology of the process. This does not mean your standing desk or mine will kill us, just that it's worth paying attention to any potential downsides developing.