If you are shooting all day events using Nikon D90 or D80, MB-D80 might be your best friend. MB-D80 battery pack simulates many buttons of your Nikon D90 and D80 camera, gives you an extended battery life and provides easy, comfort and stable holding of your camera in different orientations. Specially, if you shoot portrait photographs most of the time, MB-D80 Battery Grip can make your life much easier. It will give you nice grip and provides stability for a long day shooting. MB-D80 runs on either one or two EN-EL3e batteries or six AA-size batteries. Nikon has listed AA-size alkaline, Nickel Metal Hydride (Ni-MH), lithium and nickel-manganese as a compatible batteries for MB-D80. However, it is not compatible with non-Nikon EN-EL3e batteries.
The MB-D80 has a vertical shutter release button, main command dial (rear dial) and sub-command dial (front dial) which matches to the camera and it functions similar to the camera buttons as well. It also includes an AF-E lock button for an Autofocus exposure lock. In addition, you can also lock the shutter release button to prevent an accidental press.
Nikon D90 or D80 itself has a nice grip around the camera body but MB-D80 adds an extra grip for your camera. It is made out of very high quality materials from the Nikon products and feels solid and sturdy with the camera.
Even if there are lots of features and advantages of using it, some people are complaining about the softness of the shutter release button on MB-D80 grip. If you are used to with the camera shutter button, you may feel shutter release button on MB-D80 is little softer than real camera button and can have a chance of pressing it all the way down when you are just trying to press only halfway down for an Autofocus. But, I am sure you will be used to with it once you start using it more and more.
Some people think it looks bulky on their camera and don't want to use it. But personally, I think it adds great benefits to the camera by giving an extra battery life and an emergency backup for a long day shooting until the next recharge.