Jeff Han's TED talk - multi-touch is cool

You may have heard of multi-touch interfaces (assuming you've heard of the iPhone, then you definitely have), but might not realize just how impressive an interface development it is, or can become. To give a little background, take your old laptop trackpad and touch it with two fingers, or take an old touch screen and touch it in two places simultaneously. When you do that, a surface that isn't multi-touch capable registers your touch as being in one position central to the two contact points. A multi-touch interface notes the different locations of the multiple touch points "at once." Thereby allowing the interface magic seen here.

[via TED]