Whoever said it doesn't work, it does! It effectively charged by blackberry very quickly and turned itself off when the battery was full, so energy efficient. The only problem I have is that my blackberry case doesn't fit when the powermat back is on my phone.
Also the powermat has to be plugged in all the time to charge the phone, so you might as well just use a normal charger. I think I bought purely because of the novelty value and because it was on special offer, so was half price.
Overall, it does work, but I probably wouldn't pay full price for it.