Thom Hogan explains the proper technique for holding a Nikon DSLR camera, and how important the role played by the middle finger is:
However, I'd like to once again point out that the Nikon design is very specific to a particular ergonomic goal: being able to change controls without taking the finger off the shutter release. The proper hand position on the Nikon grip has the middle finger on the Front Command dial and the index finger arced over the shutter release in a piano-playing like position. There was a lot of ergonomic study of how to put the hand into a relaxed state but still have the three controls under fingers (thumb on Rear Command dial). Canon users learn to move their index finger off the shutter release to change a control. For a long-time Nikon user, THAT feels uncomfortable and actually slows you down shooting action.