I assume you are talking about sharing the screen live. You can mirror via AirPlay to an Apple TV, or output to an HDMI cable and plug that in to something. I have a small projector and the kids watch movies on the wall/ceiling/cat. There are a couple of types of cables that give you options. However, it doesn't do the cool dot to show that the screen has been tapped.
I found out what they use for the demos. Now i just need to know if you find a switcher like the Kanex SnapX 2x Switcher for Mac, but one with the MiniDisplayPort and the 30-Pin iPhone/iPod/iPad Connector.