OmniGod:
It's a good price, and a hot deal, but i'm not convinced by these - the standard battery on my DSLR can easily outlast the number of shots I can fir on 8Gb of CF cards, and surely if you desperately need more than that, a spare battery is a more practical solution?
I personally don't think I need one. However, it's not only abot battery life, it's also helpful when using the camera in portrait mode (holding the camera side ways) as it has wheel controls on it making the camera controls available just as they would be in normal straight landscape mode. (hope that made sense?)