One of the cool, under-publicized features of the Mac is the Apple Remote. This little fellow is barely larger than a stick of gum, but it gives you the ability to control iTunes and even Keynote presentations from across the room. Despite the fact that I have a third party "presenter" tool, I have stopped using it in my presentations because the Apple Remote is smaller and easier to use.
What happens if you lose the Remote or get a new computer that doesn’t come with one, such as the MacBook Air? As you might expect since this is an Apple product, it is easy enough to resolve this issue. You simply have to "pair" it with the optical sensor off whatever machine your using at the time. To do this, you hold "menu" and "forward" for 6 seconds. If you later want to "unpair" it, you hold "menu" and "backwards" for the same length of time. Voila!