I have been on the ball for 10 years plus. I have been using the swiss ball as a desk chair since the early 2000s. It keeps you moving on the ball, realigning your posture and allows you to do exercises while at work.
I have gone through 3 balls. I have had one pop from under me in an open plan office, after a loud bang people saw my head slowly decrease behind the desk divider to the floor. I was quite impressed my employer bought me a new ball on that occasion (its generally cheaper than a desk chair). It gets sat on 8 hours plus per day with some exercises, not to mention the bouncing and playing around when friends and colleagues get hold of it, so I think 3 years plus is not bad for the price.