I've had a swopper for a good five years or so in my home office. It's good for a time, but I ended up getting a second chair to go with it. Seems ridiculous but I like to switch between standing and sitting in various ways. I guess I just can't sit still.

I have a wobble stool that's slightly less insane than the Swopper, and I really enjoy it. Stools are great for tall people, since you can sort of lean rather than sit. Ideally, this would be coupled with an adjustable-height desk.