Thanks to Lela Kaunitz for sending me this link – I watched it and it just blew me away.

While touch sensing is commonplace for single points of contact, multi-touch sensing enables a user to interact with a system with more than one finger at a time, as in chording and bi-manual operations. Such sensing devices are inherently also able to accommodate multiple users simultaneously, which is especially useful for larger interaction scenarios such as interactive walls and tabletops.

http://mrl.nyu.edu/~jhan/ftirtouch/