Chinese pianist Lang Lang headlined a concert at San Francisco's Davies Symphony Hall on April 19th. For the first of three encores, he played The Flight of the Bumblebee on an iPad. To accomplish this, he used the Magic Piano iPad app. This is just one example of how amazing apps can allow people to do amazing things, and the party has just started.
[To clarify, the Magic Piano app does do a lot of the work in playing a piece like that; it drops down indicators for the correct notes, so the pianist has to get 'pretty close' and have the rhythm correct. Still impressive. –Ed.]