I've been using a handy little app on my iPhone lately. It comes in two versions at the moment, but more cameras, lenses, and flashguns are due soon. The next camera will be the new Nikon D5000.
The apps are clones of the Nikon D3 or D300 menu's. You navigate through the menus on your iPhone just like you do on the camera, but when you reach the end of the particular menu item, there is a description of what it actually does. It cost very little and is a great point of reference. Buy it on iTunes or go to the website at http://kentidwell.net/