I dunno if any of you has ever seen one before. But they just rolled one into the gym I go to for the attendant to sit on. I immediately thought the claim would be that it works your core while you sit on your ass. So I did a little search, and here is the claim.
So, now you can get fit by just 'sitting' on a Swiss Ball?
Saw one of these in my office the other day. It was being used by a lady who had been in a bad car accident and has to change positions every 15 minutes. She's got 4 different sections of work surface at varying heights and chairs/stools to fit each height. The ball chair thing has let her adjust to just two postures - sitting "normally" and standing. It seems not to be an item that "works" your body so much as one that hurts you less.
Had a coworker a couple years ago who sat on one, and sometimes, when he said something out of control-stupid, Me or my buddy walk over to his desk and kick it out from under him. By the time he left the office we had that fucking ball so tagged up with grotesque sharpie marker images of sexual positions and mindless movie quotes that it was deemed "unserviceable."