The huge benefit is not having to move all your stuff whenever you're done sitting or standing. I press a button and in 10 seconds it's changed height. MAGIC!
I highly suggest them to anyone, just watch out for the long backorder. Mine took 3 months to get here.
As a CTO I manage development and technology for the company, which means I'm up and around the office (and out) for meetings and touching base with other departments. If I were an engineer I'd likely utilize a standing desk less. I personally don't enjoy coding standing up.
On the Internet, nobody knows you're wearing compression stockings at your standing desk.
This coupled with an ergotron LX monitor mount and a humanscale keyboard tray is beyond fantastic. I can adjust everything, and I love it.
All in all, it probably set me back about $1000 (including the keyboard-tray and monitor-mount). And it was worth every penny; I'm much more comfortable after long hacking sessions.
[1] http://imgur.com/4XGYh [2] http://www.ikea.com/us/en/catalog/products/60057852/#/200578...
That out of the way, $1,000 for a good desk is a bargain in the long run. I'm so much more productive when I can switch between sitting and standing on a whim.
My only major concern is whether my Humanscale keyboard tray can fit underneath—it's about 21.5" long and 5.5" wide.
GeekDesk provides the dimensions of the desks, the large may not be able to accommodate your existing track, as the desk hardware mounts across the underside of the desk near the back. My 'small' frame takes up about 10" from the back of the desk, so I just got a 14" humanscale track. (My desk is only 25" wide)
This is slightly imperfect, as my tray can not fully retract under the desk, but the benefit of freeing the work surface and enabling more adjustment outweighs this concern.