The user is most likely going to use a mouse. The drawback to the mouse is that its difficult to move in more than one degree of freedom at a time. For example, you can turn right, or move down, but not both at the same time. There are many ways to map the mouse position and mouse buttons to movement. This is the way Enviro does it:
The further you are from the center of the window, the faster you move.
Hold down the left mouse button:
Hold down the right mouse button:
Hold down both mouse buttons:
If you find yourself moving too fast, keep your mouse cursor close to the center of the window, or decrease your Flight Speed. Flight speed can be controlled with toolbar buttons, shortcut keys, or the Camera dialog.
