Hmmm ... I have a home office with an Ikea-based standing desk:

http://www.flickr.com/photos/duncanbayne/7994267339/

I've since added a $75 bar stool (this sort of thing: http://www.bludot.com/media/catalog/product/cache/1/image/9d...) to sit on when my legs need a rest. It's worked well for me.