I have used doc cams for workshops and in Pro D sessions. I love that you can just plop a text book onto the screen, or demonstrate a lesson (eye dissection for example)
What is neat is that you can freeze/capture images, zoom in on them, or show things in real time, 3D, live action....
They can be pricey, but they are awesome in classrooms! I wish every class had one, along with a SMARTboard - oh the possibilities...
Check this blog out for more on doc cams