I switched to a yoga ball a few years back and my lower back pain went away completely. While sitting in general might not be ideal for long periods of time, at least with a yoga ball my back is forced to support itself, is constantly moving/adjusting and I get the adult equivalent of a bouncy chair at my desk.

For me personally it's been a great success, but I have yet to see any conclusive "yoga balls are better than chairs" articles that didn't read like new age dribble.