We've got one of those, though it was bought just before daughter's birth as a "birth ball" at exorbitant cost. As it was the labour was difficult/dangerous+++ so it was never used.

I've been advised to use it for some hyperextensions - lower back definitely a bit weak. Absolute hysteria, me rolling off and onto kitchen floor, all over the place. Totally impossible to balance. I'm now doing exercises on flat mat and they're helping the back ache.

I'm inspired too. In early August I was dreading the idea that I really should diet and exercise. Then I found DrA's NDR and then this site etc etc. I've got up early and exercised hard for the last two weeks. That really is a miracle.

Jon