You've likely seen my super cheapo standing desk. It's just one of these with a keyboard and display sitting on top:
http://www.ikea.com/gb/en/catalog/produ ... #/80178607
It looked like this until a few months ago: yes, that's a G4 iMac from all the way back in 2003!
http://deskthority.net/photos-f62/post- ... ml#p132333
I finally replaced that with a (2006 vintage) Mac Pro, and a shitty 20" Dell monitor. The old iMac was unsurpassed for adjustability. The "new" screen has none of that, so I have it sitting on top of a… drumroll…
iPod Hi-Fi! I didn't pay a dime for any of these, by the way, they're all hand me downs. But that said the iPod Hi-Fi doesn't sound too shabby at all.
The total space taken up by my standing desk is essentially zero, as it's also a fully functional chest of drawers. And I really do use it quite a bit. 50-75% of my working time. I find I'm most comfortable working upright, by far, and over the couple of years I've had it in place I've gone from needing a break every hour or so to not consciously at all. I am a fidget, though, so I'm definitely taking breaks but without noticing them. Working on your feet makes it so much more convenient to slink off for another cup of tea or what have you. In a home environment like mine, I can't recommend it enough. Work, well, it's like the clicky keyboards issue. I wonder how easily I could get by with all my IBMs!
Getting used to standing desk work did take a bit of a transition for me, though. For a while I was getting sore shoulders and a tension at the bottom of my back; lower down than the pain I was already getting from too much sitting down! I got out some old dumbbells and made a routine of shoulder exercises with those, which helped pretty quick and has given my shoulders a more pleasing look again after years of forgetting all about weights. My back pain has vanished, as far as I can tell, without any more exercise than simply standing upright for hours at a time instead of sitting.
Anyway, mix it up. With ergonomic stuff like this, everything comes down to you as as individual, and to your habits in particular. You can't change you, but you can certainly work different.