My view of the powerball is very similar to everyone else that has reviewed it. I just wanted to add something that I found very useful in addition to the great arm workout that this device gives.
I work with computers a lot, and I recently started getting RSA, Repeatative Strain Injury. It was very painful in my fingers and my wrist. However, exercising with the powerball, whenever i find these symptoms coming on, I found that the pain is lessened considerably. I don't know if it will work for everyone but in my view it is a small price to pay to alleviate the pain of RSA.