That rant over with (sorry, again), I just went to the local hardware store and got some cinder blocks. The price difference (~$7 for the cinder blocks versus ~$1000 for a height-adjustable desk frame) was worth the slight lack of convenience. That, and without the adjustability, I won't be tempted to just leave the desk in the 'down' position.
However, I did have someone with a Ph.D. in kinesiology (I think?) tell me that there's essentially no evidence of knee, hip, or back dysfunction in developing countries where people don't sit all day.
Here's a somewhat nutty article on it called "third world squat": http://www.t-nation.com/free_online_article/sports_body_trai... but it is an actual thing that people and it makes for a different muscle development than chair-dwellers have.
I think that helps me focus more, and it's probably one reason that I don't get sore from standing in one spot. Others may experience different results.
I'm a part-time stander; perhaps 25 hours per week. I also sit, recline, and every once in a while decadently lounge while reading super-important work email on my iPad. Still, I've been standing a lot for many months, so I can look back and observe:
* It takes a few weeks to feel right. I'm far past that, and I feel much less tired after standing most of the day, than sitting all day.
* Standing a lot is really not a big deal. Lots of people work on their feet all day. Every day. See the above comments about ancestors.
* It is probably possible to develop all manner of trouble by standing too still. I wouldn't know; I am essentially incapable of standing still. I shift around continuously as I work.
* It is indeed very helpful to have the monitor high enough to look straight at it; this has totally removed the incentive to slouch.