I love using stability balls for exercises. They're so versatile and fun - you can do a full body workout with just a ball and a few light weights. They're especially good for working out at home since they can double as a weight bench for many exercises.
i used to use them loads when i was playing rugby at u19 level. you can do so much with them its unreal at one point we used to stand on them and pass a ball around in a circle
I use them more for abs and flexability than weighted movements, thoug I do some of those too. THe biggest difference is no sore sine for after abs and greater range of motion in upper & lower body.