Yoga Ball - High Tech Workout Equipment, or Overpriced Balloon

Mei Mei and I purchased a big red yoga ball (roughly 30in in diameter). So far, I've determined it is really good for stretching out the back and working the ab muscles. I'm convinced it could become the cornerstone of a full body workout; I'll just need to research other ways to manipulate it. Apparently it also makes a good seat for improving one's posture. It also does a reasonable job of scaring away the cat.