I sit on Aeron chairs at work and at home (got a great deal from a former employer). I am not impressed (and I have back problems), but ergonomics is a very personal choice.
zarkdavI sit on the Leap at work, and I have to say, with how expensive it is I am not impressed. The Padding/Fabric on the back of it also comes undone quite easily. I hope it isn't the one to get dropped. But as @zarkdav said, ergonomics is a very personal choice.