So some Microsoft Research group developed this software called Songsmith which is supposed to analyse a music track and create a backing track from it which you can sing over...
The problem is the software doesn't really work leading to some unintentionally hilarious results. People have been feeding the software songs then posting the results on YouTube. Here are some examples:
Billy Idol - White Wedding
Johnny Cash - Hurt
Oasis - Wonderwall (I actually like this one.)
Survivor - Eye of the Tiger
Metallica - Battery